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æKY CopyrightNotice
æC
Larry Wall <lwall@netlabs.com>
Macintosh port by
Matthias Neeracher <neeri@iis.ethz.ch>
Tim Endres <time@ice.com>
æKY Help
PerlHelp
æKL About…Perl
Perl…Options
Perl…Types
Perl…Syntax
Perl…Compound…Statements
Perl…Simple…Statements
Perl…Expressions
Perl…Operators
Perl…Precedence
Perl…Subroutines
Perl…Regexp
Perl…Formats
Perl…IPC
Perl…Variables
Perl…Packages
Perl…Style
Perl…Debugging
Perl…Environment
Perl…Diagnostics
Perl…Traps
Perl…Errata
Perl…Bugs
Perl…Macintosh…Extensions
accept
alarm
atan2
bind
binmode
caller
chdir
chmod
choose
chop
chown
chroot
close
closedir
connect
cos
crypt
dbmclose
dbmopen
defined
delete
die
do
dump
each
endhostent
endprotoent
endservent
eof
eval
exec
exit
exp
fcntl
fileno
flock
fork
getc
gethostbyaddr
gethostbyname
gethostent
getlogin
getpeername
getprotobyname
getprotobynumber
getprotoent
getservbyname
getservbyport
getservent
getsockname
getsockopt
gmtime
goto
grep
hex
index
int
ioctl
join
keys
kill
last
length
link
listen
local
localtime
log
lstat
m
mkdir
msgctl
msgget
msgrcv
msgsnd
next
oct
open
opendir
ord
pack
pipe
pop
print
printf
push
q
rand
read
readdir
readlink
recv
redo
rename
require
reset
return
reverse
rewinddir
rindex
rmdir
s
scalar
seek
seekdir
select
semctl
semget
semop
send
setgrent
sethostent
setnetent
setpgrp
setpriority
setprotoent
setpwent
setservent
setsockopt
shift
shmctl
shmget
shmread
shutdown
sin
sleep
socket
socketpair
sort
splice
split
sprintf
sqrt
srand
stat
study
substr
symlink
syscall
sysread
system
syswrite
tell
telldir
time
times
tr
truncate
umask
undef
unlink
unpack
unshift
utime
values
vec
wait
waitpid
wantarray
warn
write
æKY MacPerl…Help
æC
Welcome to MacPerl!
To use the online help, select a word in a window and select this
Help command. For an overview of available help topics, select "Help"
and select the Help command.
æKY Perl
About…Perl
æC
Perl -- Practical Extraction and Report Language
Perl is an interpreted language optimized for scanning arbitrary
text files, extracting information from those text files, and
printing reports based on that information. It's also a good
language for many system management tasks. The language is intended
to be practical (easy to use, efficient, complete) rather than
beautiful (tiny, elegant, minimal). It combines (in the author's
opinion, anyway) some of the best features of C, sed, awk, and sh,
so people familiar with those languages should have little
difficulty with it. (Language historians will also note some
vestiges of csh, Pascal, and even BASIC-PLUS.) Expression syntax
corresponds quite closely to C expression syntax. Unlike most Unix
utilities, perl does not arbitrarily limit the size of your data--if
you've got the memory, perl can slurp in your whole file as a single
string. Recursion is of unlimited depth. And the hash tables used by
associative arrays grow as necessary to prevent degraded performance.
Perl uses sophisti- cated pattern matching techniques to scan large
amounts of data very quickly. Although optimized for scanning text,
perl can also deal with binary data, and can make dbm files look like
associative arrays (where dbm is available). Setuid perl scripts are
safer than C programs through a dataflow tracing mechanism which
prevents many stupid security holes. If you have a problem that
would ordinarily use sed or awk or sh, but it exceeds their
capabilities or must run a little faster, and you don't want to write
the silly thing in C, then perl may be for you. There are also
translators to turn your sed and awk scripts into perl scripts.
OK, enough hype.
Upon startup, perl looks for your script in one of the following
places:
1. Specified line by line via -e switches on the command line.
2. Contained in the file specified by the first filename on the
command line. (Note that systems supporting the #! notation
invoke interpreters this way.)
3. Passed in implicitly via standard input. This only works if
there are no filename arguments--to pass arguments to a stdin
script you must explicitly specify a - for the script name.
After locating your script, perl compiles it to an internal form.
If the script is syntactically correct, it is executed.
æKY Perl…Options
æC
A single-character option may be combined with the following
option, if any. This is particularly useful when invoking a
script using the #! construct which only allows one argument.
Example:
#!/usr/bin/perl -spi.bak # same as -s -p -i.bak
...
Options include:
-0digits
specifies the record separator ($/) as an octal number. If
there are no digits, the null character is the separator.
Other switches may precede or follow the digits. For exam-
ple, if you have a version of find which can print filenames
terminated by the null character, you can say this:
find . -name '*.bak' -print0 | perl -n0e unlink
The special value 00 will cause Perl to slurp files in para-
graph mode. The value 0777 will cause Perl to slurp files
whole since there is no legal character with that value.
-a turns on autosplit mode when used with a -n or -p. An
implicit split command to the @F array is done as the first
thing inside the implicit while loop produced by the -n or -p.
perl -ane 'print pop(@F), "\n";'
is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}
-c causes perl to check the syntax of the script and then exit
without executing it.
-d runs the script under the perl debugger. See the section on
Debugging.
-Dnumber
sets debugging flags. To watch how it executes your script,
use -D14. (This only works if debugging is compiled into
your perl.) Another nice value is -D1024, which lists your
compiled syntax tree. And -D512 displays compiled regular
expressions.
-e commandline
may be used to enter one line of script. Multiple -e com-
mands may be given to build up a multi-line script. If -e
is given, perl will not look for a script filename in the
argument list.
-iextension
specifies that files processed by the <> construct are to be
edited in-place. It does this by renaming the input file,
opening the output file by the same name, and selecting that
output file as the default for print statements. The exten-
sion, if supplied, is added to the name of the old file to
make a backup copy. If no extension is supplied, no backup
is made. Saying "perl -p -i.bak -e "s/foo/bar/;" ... " is
the same as using the script:
#!/usr/bin/perl -pi.bak
s/foo/bar/;
which is equivalent to
#!/usr/bin/perl
while (<>) {
if ($ARGV ne $oldargv) {
rename($ARGV, $ARGV . '.bak');
open(ARGVOUT, ">$ARGV");
select(ARGVOUT);
$oldargv = $ARGV;
}
s/foo/bar/;
}
continue {
print; # this prints to original filename
}
select(STDOUT);
except that the -i form doesn't need to compare $ARGV to
$oldargv to know when the filename has changed. It does,
however, use ARGVOUT for the selected filehandle. Note that
STDOUT is restored as the default output filehandle after
the loop.
You can use eof to locate the end of each input file, in
case you want to append to each file, or reset line number-
ing (see example under eof).
-Idirectory
may be used in conjunction with -P to tell the C preproces-
sor where to look for include files. By default
/usr/include and /usr/lib/perl are searched.
-loctnum
enables automatic line-ending processing. It has two
effects: first, it automatically chops the line terminator
when used with -n or -p , and second, it assigns $\ to have
the value of octnum so that any print statements will have
that line terminator added back on. If octnum is omitted,
sets $\ to the current value of $/. For instance, to trim
lines to 80 columns:
perl -lpe 'substr($_, 80) = ""'
Note that the assignment $\ = $/ is done when the switch is
processed, so the input record separator can be different
than the output record separator if the -l switch is fol-
lowed by a -0 switch:
gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
This sets $\ to newline and then sets $/ to the null charac-
ter.
-n causes perl to assume the following loop around your script,
which makes it iterate over filename arguments somewhat like
"sed -n" or awk:
while (<>) {
... # your script goes here
}
Note that the lines are not printed by default. See -p to
have lines printed. Here is an efficient way to delete all
files older than a week:
find . -mtime +7 -print | perl -nle 'unlink;'
This is faster than using the -exec switch of find because
you don't have to start a process on every filename found.
-p causes perl to assume the following loop around your script,
which makes it iterate over filename arguments somewhat like
sed:
while (<>) {
... # your script goes here
} continue {
print;
}
Note that the lines are printed automatically. To suppress
printing use the -n switch. A -p overrides a -n switch.
-P causes your script to be run through the C preprocessor
before compilation by perl. (Since both comments and cpp
directives begin with the # character, you should avoid
starting comments with any words recognized by the C prepro-
cessor such as "if", "else" or "define".)
-s enables some rudimentary switch parsing for switches on the
command line after the script name but before any filename
arguments (or before a --). Any switch found there is
removed from @ARGV and sets the corresponding variable in
the perl script. The following script prints "true" if and
only if the script is invoked with a -xyz switch.
#!/usr/bin/perl -s
if ($xyz) { print "true\n"; }
-S makes perl use the PATH environment variable to search for
the script (unless the name of the script starts with a
slash). Typically this is used to emulate #! startup on
machines that don't support #!, in the following manner:
#!/usr/bin/perl
eval "exec /usr/bin/perl -S $0 $*"
if $running_under_some_shell;
The system ignores the first line and feeds the script to
/bin/sh, which proceeds to try to execute the perl script as
a shell script. The shell executes the second line as a
normal shell command, and thus starts up the perl inter-
preter. On some systems $0 doesn't always contain the full
pathname, so the -S tells perl to search for the script if
necessary. After perl locates the script, it parses the
lines and ignores them because the variable
$running_under_some_shell is never true. A better construct
than $* would be ${1+"$@"}, which handles embedded spaces
and such in the filenames, but doesn't work if the script is
being interpreted by csh. In order to start up sh rather
than csh, some systems may have to replace the #! line with
a line containing just a colon, which will be politely
ignored by perl. Other systems can't control that, and need
a totally devious construct that will work under any of csh,
sh or perl, such as the following:
eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
& eval 'exec /usr/bin/perl -S $0 $argv:q'
if 0;
-u causes perl to dump core after compiling your script. You
can then take this core dump and turn it into an executable
file by using the undump program (not supplied). This
speeds startup at the expense of some disk space (which you
can minimize by stripping the executable). (Still, a "hello
world" executable comes out to about 200K on my machine.) If
you are going to run your executable as a set-id program
then you should probably compile it using taintperl rather
than normal perl. If you want to execute a portion of your
script before dumping, use the dump operator instead. Note:
availability of undump is platform specific and may not be
available for a specific port of perl.
-U allows perl to do unsafe operations. Currently the only
"unsafe" operation is the unlinking of directories while
running as superuser.
-v prints the version and patchlevel of your perl executable.
-w prints warnings about identifiers that are mentioned only
once, and scalar variables that are used before being set.
Also warns about redefined subroutines, and references to
undefined filehandles or filehandles opened readonly that
you are attempting to write on. Also warns you if you use
== on values that don't look like numbers, and if your sub-
routines recurse more than 100 deep.
-xdirectory
tells perl that the script is embedded in a message. Lead-
ing garbage will be discarded until the first line that
starts with #! and contains the string "perl". Any meaning-
ful switches on that line will be applied (but only one
group of switches, as with normal #! processing). If a
directory name is specified, Perl will switch to that direc-
tory before running the script. The -x switch only controls
the the disposal of leading garbage. The script must be
terminated with __END__ if there is trailing garbage to be
ignored (the script can process any or all of the trailing
garbage via the DATA filehandle if desired).
æKY Perl…Types
æC
Perl has three data types: scalars, arrays of scalars, and asso-
ciative arrays of scalars. Normal arrays are indexed by number,
and associative arrays by string.
The interpretation of operations and values in perl sometimes
depends on the requirements of the context around the operation
or value. There are three major contexts: string, numeric and
array. Certain operations return array values in contexts want-
ing an array, and scalar values otherwise. (If this is true of
an operation it will be mentioned in the documentation for that
operation.) Operations which return scalars don't care whether
the context is looking for a string or a number, but scalar vari-
ables and values are interpreted as strings or numbers as
appropriate to the context. A scalar is interpreted as TRUE in
the boolean sense if it is not the null string or 0. Booleans
returned by operators are 1 for true and 0 or '' (the null
string) for false.
There are actually two varieties of null string: defined and
undefined. Undefined null strings are returned when there is no
real value for something, such as when there was an error, or at
end of file, or when you refer to an uninitialized variable or
element of an array. An undefined null string may become defined
the first time you access it, but prior to that you can use the
defined() operator to determine whether the value is defined or
not.
References to scalar variables always begin with '$', even when
referring to a scalar that is part of an array. Thus:
$days # a simple scalar variable
$days[28] # 29th element of array @days
$days{'Feb'} # one value from an associative array
$#days # last index of array @days
but entire arrays or array slices are denoted by '@':
@days # ($days[0], $days[1],... $days[n])
@days[3,4,5] # same as @days[3..5]
@days{'a','c'} # same as ($days{'a'},$days{'c'})
and entire associative arrays are denoted by '%':
%days # (key1, val1, key2, val2 ...)
Any of these eight constructs may serve as an lvalue, that is,
may be assigned to. (It also turns out that an assignment is
itself an lvalue in certain contexts--see examples under s, tr
and chop.) Assignment to a scalar evaluates the righthand side in
a scalar context, while assignment to an array or array slice
evaluates the righthand side in an array context.
You may find the length of array @days by evaluating "$#days", as
in csh. (Actually, it's not the length of the array, it's the
subscript of the last element, since there is (ordinarily) a 0th
element.) Assigning to $#days changes the length of the array.
Shortening an array by this method does not actually destroy any
values. Lengthening an array that was previously shortened
recovers the values that were in those elements. You can also
gain some measure of efficiency by preextending an array that is
going to get big. (You can also extend an array by assigning to
an element that is off the end of the array. This differs from
assigning to $#whatever in that intervening values are set to
null rather than recovered.) You can truncate an array down to
nothing by assigning the null list () to it. The following are
exactly equivalent
@whatever = ();
$#whatever = $[ - 1;
If you evaluate an array in a scalar context, it returns the
length of the array. The following is always true:
scalar(@whatever) == $#whatever - $[ + 1;
If you evaluate an associative array in a scalar context, it returns
a value which is true if and only if the array contains any elements.
(If there are any elements, the value returned is a string consisting
of the number of used buckets and the number of allocated buckets,
separated by a slash.)
Multi-dimensional arrays are not directly supported, but see the
discussion of the $; variable later for a means of emulating mul-
tiple subscripts with an associative array. You could also write
a subroutine to turn multiple subscripts into a single subscript.
Every data type has its own namespace. You can, without fear of
conflict, use the same name for a scalar variable, an array, an
associative array, a filehandle, a subroutine name, and/or a
label. Since variable and array references always start with
'$', '@', or '%', the "reserved" words aren't in fact reserved
with respect to variable names. (They ARE reserved with respect
to labels and filehandles, however, which don't have an initial
special character. Hint: you could say open(LOG,'logfile')
rather than open(log,'logfile'). Using uppercase filehandles
also improves readability and protects you from conflict with
future reserved words.) Case IS significant--"FOO", "Foo" and
"foo" are all different names. Names which start with a letter
may also contain digits and underscores. Names which do not
start with a letter are limited to one character, e.g. "$%" or
"$$". (Most of the one character names have a predefined signi-
ficance to perl. More later.)
Numeric literals are specified in any of the usual floating point
or integer formats:
12345
12345.67
.23E-10
0xffff # hex
0377 # octal
4_294_967_296
String literals are delimited by either single or double quotes.
They work much like shell quotes: double-quoted string literals
are subject to backslash and variable substitution; single-quoted
strings are not (except for \' and \\). The usual backslash
rules apply for making characters such as newline, tab, etc., as
well as some more exotic forms:
\t tab
\n newline
\r return
\f form feed
\b backspace
\a alarm (bell)
\e escape
\033 octal char
\x1b hex char
\c[ control char
\l lowercase next char
\u uppercase next char
\L lowercase till \E
\U uppercase till \E
\E end case modification
You can also embed newlines directly in your strings, i.e. they
can end on a different line than they begin. This is nice, but
if you forget your trailing quote, the error will not be reported
until perl finds another line containing the quote character,
which may be much further on in the script. Variable substitu-
tion inside strings is limited to scalar variables, normal array
values, and array slices. (In other words, identifiers beginning
with $ or @, followed by an optional bracketed expression as a
subscript.) The following code segment prints out "The price is
$100."
$Price = '$100'; # not interpreted
print "The price is $Price.\n";# interpreted
Note that you can put curly brackets around the identifier to
delimit it from following alphanumerics. Also note that a single
quoted string must be separated from a preceding word by a space,
since single quote is a valid character in an identifier (see
Packages).
Two special literals are __LINE__ and __FILE__, which represent
the current line number and filename at that point in your pro-
gram. They may only be used as separate tokens; they will not be
interpolated into strings. In addition, the token __END__ may be
used to indicate the logical end of the script before the actual
end of file. Any following text is ignored, but may be read via
the DATA filehandle. (The DATA filehandle may read data only from
the main script, but not from any required file or evaluated string.)
The two control characters ^D and ^Z are synonyms for __END__.
A word that doesn't have any other interpretation in the grammar
will be treated as if it had single quotes around it. For this
purpose, a word consists only of alphanumeric characters and
underline, and must start with an alphabetic character. As with
filehandles and labels, a bare word that consists entirely of
lowercase letters risks conflict with future reserved words, and
if you use the -w switch, Perl will warn you about any such
words.
Array values are interpolated into double-quoted strings by join-
ing all the elements of the array with the delimiter specified in
the $" variable, space by default. (Since in versions of perl
prior to 3.0 the @ character was not a metacharacter in double-
quoted strings, the interpolation of @array, $array[EXPR],
@array[LIST], $array{EXPR}, or @array{LIST} only happens if array
is referenced elsewhere in the program or is predefined.) The
following are equivalent:
$temp = join($",@ARGV);
system "echo $temp";
system "echo @ARGV";
Within search patterns (which also undergo double-quotish substi-
tution) there is a bad ambiguity: Is /$foo[bar]/ to be inter-
preted as /${foo}[bar]/ (where [bar] is a character class for the
regular expression) or as /${foo[bar]}/ (where [bar] is the sub-
script to array @foo)? If @foo doesn't otherwise exist, then
it's obviously a character class. If @foo exists, perl takes a
good guess about [bar], and is almost always right. If it does
guess wrong, or if you're just plain paranoid, you can force the
correct interpretation with curly brackets as above.
A line-oriented form of quoting is based on the shell here-is
syntax. Following a << you specify a string to terminate the
quoted material, and all lines following the current line down to
the terminating string are the value of the item. The terminat-
ing string may be either an identifier (a word), or some quoted
text. If quoted, the type of quotes you use determines the
treatment of the text, just as in regular quoting. An unquoted
identifier works like double quotes. There must be no space
between the << and the identifier. (If you put a space it will
be treated as a null identifier, which is valid, and matches the
first blank line--see Merry Christmas example below.) The ter-
minating string must appear by itself (unquoted and with no sur-
rounding whitespace) on the terminating line.
print <<EOF; # same as above
The price is $Price.
EOF
print <<"EOF"; # same as above
The price is $Price.
EOF
print << x 10; # null identifier is delimiter
Merry Christmas!
print <<`EOC`; # execute commands
echo hi there
echo lo there
EOC
print <<foo, <<bar; # you can stack them
I said foo.
foo
I said bar.
bar
Array literals are denoted by separating individual values by
commas, and enclosing the list in parentheses:
(LIST)
In a context not requiring an array value, the value of the array
literal is the value of the final element, as in the C comma
operator. For example,
@foo = ('cc', '-E', $bar);
assigns the entire array value to array foo, but
$foo = ('cc', '-E', $bar);
assigns the value of variable bar to variable foo. Note that the
value of an actual array in a scalar context is the length of the
array; the following assigns to $foo the value 3:
@foo = ('cc', '-E', $bar);
$foo = @foo; # $foo gets 3
You may have an optional comma before the closing parenthesis of
an array literal, so that you can say:
@foo = (
1,
2,
3,
);
When a LIST is evaluated, each element of the list is evaluated
in an array context, and the resulting array value is interpo-
lated into LIST just as if each individual element were a member
of LIST. Thus arrays lose their identity in a LIST--the list
(@foo,@bar,&SomeSub)
contains all the elements of @foo followed by all the elements of
@bar, followed by all the elements returned by the subroutine
named SomeSub.
A list value may also be subscripted like a normal array. Exam-
ples:
$time = (stat($file))[8]; # stat returns array value
$digit = ('a','b','c','d','e','f')[$digit-10];
return (pop(@foo),pop(@foo))[0];
Array lists may be assigned to if and only if each element of the
list is an lvalue:
($a, $b, $c) = (1, 2, 3);
($map{'red'}, $map{'blue'}, $map{'green'}) = (0x00f, 0x0f0, 0xf00);
The final element may be an array or an associative array:
($a, $b, @rest) = split;
local($a, $b, %rest) = @_;
You can actually put an array anywhere in the list, but the first
array in the list will soak up all the values, and anything after
it will get a null value. This may be useful in a local().
An associative array literal contains pairs of values to be
interpreted as a key and a value:
# same as map assignment above
%map = ('red',0x00f,'blue',0x0f0,'green',0xf00);
Array assignment in a scalar context returns the number of ele-
ments produced by the expression on the right side of the assign-
ment:
$x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2
There are several other pseudo-literals that you should know
about. If a string is enclosed by backticks (grave accents), it
first undergoes variable substitution just like a double quoted
string. It is then interpreted as a command, and the output of
that command is the value of the pseudo-literal, like in a shell.
In a scalar context, a single string consisting of all the output
is returned. In an array context, an array of values is
returned, one for each line of output. (You can set $/ to use a
different line terminator.) The command is executed each time the
pseudo-literal is evaluated. The status value of the command is
returned in $? (see Predefined Names for the interpretation of
$?). Unlike in csh, no translation is done on the return data--
newlines remain newlines. Unlike in any of the shells, single
quotes do not hide variable names in the command from interpreta-
tion. To pass a $ through to the shell you need to hide it with
a backslash.
Evaluating a filehandle in angle brackets yields the next line
from that file (newline included, so it's never false until EOF,
at which time an undefined value is returned). Ordinarily you
must assign that value to a variable, but there is one situation
where an automatic assignment happens. If (and only if) the
input symbol is the only thing inside the conditional of a while
loop, the value is automatically assigned to the variable "$_".
(This may seem like an odd thing to you, but you'll use the con-
struct in almost every perl script you write.) Anyway, the fol-
lowing lines are equivalent to each other:
while ($_ = <STDIN>) { print; }
while (<STDIN>) { print; }
for (;<STDIN>;) { print; }
print while $_ = <STDIN>;
print while <STDIN>;
The filehandles STDIN, STDOUT and STDERR are predefined. (The
filehandles stdin, stdout and stderr will also work except in
packages, where they would be interpreted as local identifiers
rather than global.) Additional filehandles may be created with
the open function.
If a <FILEHANDLE> is used in a context that is looking for an
array, an array consisting of all the input lines is returned,
one line per array element. It's easy to make a LARGE data space
this way, so use with care.
The null filehandle <> is special and can be used to emulate the
behavior of sed and awk. Input from <> comes either from stan-
dard input, or from each file listed on the command line. Here's
how it works: the first time <> is evaluated, the ARGV array is
checked, and if it is null, $ARGV[0] is set to '-', which when
opened gives you standard input. The ARGV array is then pro-
cessed as a list of filenames. The loop
while (<>) {
... # code for each line
}
is equivalent to the following Perl-like pseudo code:
unshift(@ARGV, '-') if $#ARGV < $[;
while ($ARGV = shift) {
open(ARGV, $ARGV);
while (<ARGV>) {
... # code for each line
}
}
except that it isn't as cumbersome to say, and will actually
work. It really does shift array ARGV and put the current
filename into variable ARGV. It also uses filehandle ARGV
internally -- <> is just a synonym for <ARGV>, which is magical.
(The pseudo code above doesn't work because it treats <ARGV> as
non-magical.)
You can modify @ARGV before the first <> as long as the array ends up
containing the list of filenames you really want.
Line numbers ($.) continue as if the input was one big happy file.
(But see example under eof for how to reset line numbers on each file.)
If you want to set @ARGV to your own list of files, go right
ahead. If you want to pass switches into your script, you can
put a loop on the front like this:
while ($_ = $ARGV[0], /^-/) {
shift;
last if /^--$/;
/^-D(.*)/ && ($debug = $1);
/^-v/ && $verbose++;
... # other switches
}
while (<>) {
... # code for each line
}
The <> symbol will return FALSE only once. If you call it again
after this it will assume you are processing another @ARGV list,
and if you haven't set @ARGV, will input from STDIN.
If the string inside the angle brackets is a reference to a
scalar variable (e.g. <$foo>), then that variable contains the
name of the filehandle to input from.
If the string inside angle brackets is not a filehandle, it is
interpreted as a filename pattern to be globbed, and either an
array of filenames or the next filename in the list is returned,
depending on context. One level of $ interpretation is done
first, but you can't say <$foo> because that's an indirect
filehandle as explained in the previous paragraph. You could
insert curly brackets to force interpretation as a filename glob:
<${foo}>. Example:
while (<*.c>) {
chmod 0644, $_;
}
is equivalent to
open(foo, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|");
while (<foo>) {
chop;
chmod 0644, $_;
}
In fact, it's currently implemented that way. (Which means it
will not work on filenames with spaces in them unless you have
/bin/csh on your machine.) Of course, the shortest way to do the
above is:
chmod 0644, <*.c>;
æKY Perl…Syntax
æC
A perl script consists of a sequence of declarations and com-
mands. The only things that need to be declared in perl are
report formats and subroutines. See the sections below for more
information on those declarations. All uninitialized user-
created objects are assumed to start with a null or 0 value until
they are defined by some explicit operation such as assignment.
The sequence of commands is executed just once, unlike in sed and
awk scripts, where the sequence of commands is executed for each
input line. While this means that you must explicitly loop over
the lines of your input file (or files), it also means you have
much more control over which files and which lines you look at.
(Actually, I'm lying--it is possible to do an implicit loop with
either the -n or -p switch.)
A declaration can be put anywhere a command can, but has no
effect on the execution of the primary sequence of commands--
declarations all take effect at compile time. Typically all the
declarations are put at the beginning or the end of the script.
Perl is, for the most part, a free-form language. (The only
exception to this is format declarations, for fairly obvious rea-
sons.) Comments are indicated by the # character, and extend to
the end of the line. If you attempt to use /* */ C comments, it
will be interpreted either as division or pattern matching,
depending on the context. So don't do that.
SEE ALSO
æKL Perl…Compound…Statements
Perl…Simple…Statements
Perl…Expressions
æKY Perl…Compound…Statements
æC
In perl, a sequence of commands may be treated as one command by
enclosing it in curly brackets. We will call this a BLOCK.
The following compound commands may be used to control flow:
if (EXPR) BLOCK
if (EXPR) BLOCK else BLOCK
if (EXPR) BLOCK elsif (EXPR) BLOCK ... else BLOCK
LABEL while (EXPR) BLOCK
LABEL while (EXPR) BLOCK continue BLOCK
LABEL for (EXPR; EXPR; EXPR) BLOCK
LABEL foreach VAR (ARRAY) BLOCK
LABEL BLOCK continue BLOCK
Note that, unlike C and Pascal, these are defined in terms of
BLOCKs, not statements. This means that the curly brackets are
required--no dangling statements allowed. If you want to write
conditionals without curly brackets there are several other ways
to do it. The following all do the same thing:
if (!open(foo)) { die "Can't open $foo: $!"; }
die "Can't open $foo: $!" unless open(foo);
open(foo) || die "Can't open $foo: $!"; # foo or bust!
open(foo) ? 'hi mom' : die "Can't open $foo: $!";
# a bit exotic, that last one
The if statement is straightforward. Since BLOCKs are always
bounded by curly brackets, there is never any ambiguity about
which if an else goes with. If you use unless in place of if,
the sense of the test is reversed.
The while statement executes the block as long as the expression
is true (does not evaluate to the null string or 0). The LABEL
is optional, and if present, consists of an identifier followed
by a colon. The LABEL identifies the loop for the loop control
statements next, last, and redo (see below). If there is a con-
tinue BLOCK, it is always executed just before the conditional is
about to be evaluated again, similarly to the third part of a for
loop in C. Thus it can be used to increment a loop variable,
even when the loop has been continued via the next statement
(similar to the C "continue" statement).
If the word while is replaced by the word until, the sense of the
test is reversed, but the conditional is still tested before the
first iteration.
In either the if or the while statement, you may replace "(EXPR)"
with a BLOCK, and the conditional is true if the value of the
last command in that block is true.
The for loop works exactly like the corresponding while loop:
for ($i = 1; $i < 10; $i++) {
...
}
is the same as
$i = 1;
while ($i < 10) {
...
} continue {
$i++;
}
The foreach loop iterates over a normal array value and sets the
variable VAR to be each element of the array in turn. The vari-
able is implicitly local to the loop, and regains its former
value upon exiting the loop. The "foreach" keyword is actually
identical to the "for" keyword, so you can use "foreach" for rea-
dability or "for" for brevity. If VAR is omitted, $_ is set to
each value. If ARRAY is an actual array (as opposed to an
expression returning an array value), you can modify each element
of the array by modifying VAR inside the loop. Examples:
for (@ary) { s/foo/bar/; }
foreach $elem (@elements) {
$elem *= 2;
}
for ((10,9,8,7,6,5,4,3,2,1,'BOOM')) {
print $_, "\n"; sleep(1);
}
for (1..15) { print "Merry Christmas\n"; }
foreach $item (split(/:[\\\n:]*/, $ENV{'TERMCAP'})) {
print "Item: $item\n";
}
The BLOCK by itself (labeled or not) is equivalent to a loop that
executes once. Thus you can use any of the loop control state-
ments in it to leave or restart the block. The continue block is
optional. This construct is particularly nice for doing case
structures.
foo: {
if (/^abc/) { $abc = 1; last foo; }
if (/^def/) { $def = 1; last foo; }
if (/^xyz/) { $xyz = 1; last foo; }
$nothing = 1;
}
There is no official switch statement in perl, because there are
already several ways to write the equivalent. In addition to the
above, you could write
foo: {
$abc = 1, last foo if /^abc/;
$def = 1, last foo if /^def/;
$xyz = 1, last foo if /^xyz/;
$nothing = 1;
}
or
foo: {
/^abc/ && do { $abc = 1; last foo; };
/^def/ && do { $def = 1; last foo; };
/^xyz/ && do { $xyz = 1; last foo; };
$nothing = 1;
}
or
foo: {
/^abc/ && ($abc = 1, last foo);
/^def/ && ($def = 1, last foo);
/^xyz/ && ($xyz = 1, last foo);
$nothing = 1;
}
or even
if (/^abc/)
{ $abc = 1; }
elsif (/^def/)
{ $def = 1; }
elsif (/^xyz/)
{ $xyz = 1; }
else
{$nothing = 1;}
As it happens, these are all optimized internally to a switch
structure, so perl jumps directly to the desired statement, and
you needn't worry about perl executing a lot of unnecessary
statements when you have a string of 50 elsifs, as long as you
are testing the same simple scalar variable using ==, eq, or pat-
tern matching as above. (If you're curious as to whether the
optimizer has done this for a particular case statement, you can
use the -D1024 switch to list the syntax tree before execution.)
æKY Perl…Simple…Statements
æC
The only kind of simple statement is an expression evaluated for
its side effects. Every simple statement must be terminated with a
semicolon, unless it is the final statement in a block, in which case
the semicolon is optional. (Semicolon is still encouraged there if the
block takes up more than one line).
Any simple statement may optionally be followed by a single
modifier, just before the terminating semicolon. The possible
modifiers are:
if EXPR
unless EXPR
while EXPR
until EXPR
The if and unless modifiers have the expected semantics. The
while and until modifiers also have the expected semantics (con-
ditional evaluated first), except when applied to a do-BLOCK or a
do-SUBROUTINE command, in which case the block executes once
before the conditional is evaluated. This is so that you can
write loops like:
do {
$_ = <STDIN>;
...
} until $_ eq ".\n";
(See the do operator below. Note also that the loop control com-
mands described later will NOT work in this construct, since
modifiers don't take loop labels. Sorry.)
æKY Perl…Expressions
æC
Since perl expressions work almost exactly like C expressions,
only the differences will be mentioned here.
Here's what perl has that C doesn't:
** The exponentiation operator.
**= The exponentiation assignment operator.
() The null list, used to initialize an array to null.
. Concatenation of two strings.
.= The concatenation assignment operator.
eq String equality (== is numeric equality). For a mnemonic
just think of "eq" as a string. (If you are used to the
awk behavior of using == for either string or numeric
equality based on the current form of the comparands,
beware! You must be explicit here.)
ne String inequality (!= is numeric inequality).
lt String less than.
gt String greater than.
le String less than or equal.
ge String greater than or equal.
cmp String comparison, returning -1, 0, or 1.
<=> Numeric comparison, returning -1, 0, or 1.
=~ Certain operations search or modify the string "$_" by
default. This operator makes that kind of operation work
on some other string. The right argument is a search
pattern, substitution, or translation. The left argument
is what is supposed to be searched, substituted, or
translated instead of the default "$_". The return value
indicates the success of the operation. (If the right
argument is an expression other than a search pattern,
substitution, or translation, it is interpreted as a
search pattern at run time. This is less efficient than
an explicit search, since the pattern must be compiled
every time the expression is evaluated.) The precedence
of this operator is lower than unary minus and
autoincrement/decrement, but higher than everything else.
!~ Just like =~ except the return value is negated.
x The repetition operator. Returns a string consisting of
the left operand repeated the number of times specified
by the right operand. In an array context, if the left
operand is a list in parens, it repeats the list.
print '-' x 80; # print row of dashes
print '-' x80; # illegal, x80 is identifier
print "\t" x ($tab/8), ' ' x ($tab%8); # tab over
@ones = (1) x 80; # an array of 80 1's
@ones = (5) x @ones; # set all elements to 5
x= The repetition assignment operator. Only works on
scalars.
.. The range operator, which is really two different opera-
tors depending on the context. In an array context,
returns an array of values counting (by ones) from the
left value to the right value. This is useful for writ-
ing "for (1..10)" loops and for doing slice operations on
arrays.
In a scalar context, .. returns a boolean value. The
operator is bistable, like a flip-flop, and emulates the
line-range (comma) operator of sed, awk, and various
editors. Each .. opera tor maintains its own boolean state.
It is false as long as its left operand is false. Once the
left operand is true, the range operator stays true until
the right operand is true, AFTER which the range operator
becomes false again. (It doesn't become false till the next
time the range operator is evaluated. It can test the right
operand and become false on the same evaluation it became
true (as in awk), but it still returns true once. If you don't
want it to test the right operand till the next evaluation
(as in sed), use three dots (...) instead of two.) The right
operand is not evaluated while the operator is in the "false"
state, and the left operand is not evaluated while the operator
is in the "true" state. The precedence is a little lower than
|| and &&. The value returned is either the null string for
false, or a sequence number (beginning with 1) for true. The
sequence number is reset for each range encountered. The final
sequence number in a range has the string 'E0' appended to it,
which doesn't affect its numeric value, but gives you something
to search for if you want to exclude the endpoint. You can
exclude the beginning point by waiting for the sequence number
to be greater than 1. If either operand of scalar .. is static,
that operand is implicitly compared to the $. variable, the
current line number. Examples:
As a scalar operator:
if (101 .. 200) { print; } # print 2nd hundred lines
next line if (1 .. /^$/); # skip header lines
s/^/> / if (/^$/ .. eof()); # quote body
As an array operator:
for (101 .. 200) { print; } # print $_ 100 times
@foo = @foo[$[ .. $#foo]; # an expensive no-op
@foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items
-x A file test. This unary operator takes one argument,
either a filename or a filehandle, and tests the associ-
ated file to see if something is true about it. If the
argument is omitted, tests $_, except for -t, which tests
STDIN. It returns 1 for true and '' for false, or the
undefined value if the file doesn't exist. Precedence is
higher than logical and relational operators, but lower
than arithmetic operators. The operator may be any of:
-r File is readable by effective uid/gid.
-w File is writable by effective uid/gid.
-x File is executable by effective uid/gid.
-o File is owned by effective uid.
-R File is readable by real uid/gid.
-W File is writable by real uid/gid.
-X File is executable by real uid/gid.
-O File is owned by real uid.
-e File exists.
-z File has zero size.
-s File has non-zero size (returns size).
-f File is a plain file.
-d File is a directory.
-l File is a symbolic link.
-p File is a named pipe (FIFO).
-S File is a socket.
-b File is a block special file.
-c File is a character special file.
-u File has setuid bit set.
-g File has setgid bit set.
-k File has sticky bit set.
-t Filehandle is opened to a tty.
-T File is a text file.
-B File is a binary file (opposite of -T).
-M Age of file in days when script started.
-A Same for access time.
-C Same for inode change time.
The interpretation of the file permission operators -r,
-R, -w, -W, -x and -X is based solely on the mode of the
file and the uids and gids of the user. There may be
other reasons you can't actually read, write or execute
the file. Also note that, for the superuser, -r, -R, -w
and -W always return 1, and -x and -X return 1 if any
execute bit is set in the mode. Scripts run by the
superuser may thus need to do a stat() in order to deter-
mine the actual mode of the file, or temporarily set the
uid to something else.
Example:
while (<>) {
chop;
next unless -f $_; # ignore specials
...
}
Note that -s/a/b/ does not do a negated substitution.
Saying -exp($foo) still works as expected, however--only
single letters following a minus are interpreted as file
tests.
The -T and -B switches work as follows. The first block
or so of the file is examined for odd characters such as
strange control codes or metacharacters. If too many odd
characters (>10%) are found, it's a -B file, otherwise
it's a -T file. Also, any file containing null in the
first block is considered a binary file. If -T or -B is
used on a filehandle, the current stdio buffer is exam-
ined rather than the first block. Both -T and -B return
TRUE on a null file, or a file at EOF when testing a
filehandle.
If any of the file tests (or either stat operator) are given the
special filehandle consisting of a solitary underline, then the
stat structure of the previous file test (or stat operator) is
used, saving a system call. (This doesn't work with -t, and you
need to remember that lstat and -l will leave values in the stat
structure for the symbolic link, not the real file.) Example:
print "Can do.\n" if -r $a || -w _ || -x _;
stat($filename);
print "Readable\n" if -r _;
print "Writable\n" if -w _;
print "Executable\n" if -x _;
print "Setuid\n" if -u _;
print "Setgid\n" if -g _;
print "Sticky\n" if -k _;
print "Text\n" if -T _;
print "Binary\n" if -B _;
Here is what C has that perl doesn't:
unary & Address-of operator.
unary * Dereference-address operator.
(TYPE) Type casting operator.
Like C, perl does a certain amount of expression evaluation at
compile time, whenever it determines that all of the arguments to
an operator are static and have no side effects. In particular,
string concatenation happens at compile time between literals
that don't do variable substitution. Backslash interpretation
also happens at compile time. You can say
'Now is the time for all' . "\n" .
'good men to come to.'
and this all reduces to one string internally.
The autoincrement operator has a little extra built-in magic to
it. If you increment a variable that is numeric, or that has
ever been used in a numeric context, you get a normal increment.
If, however, the variable has only been used in string contexts
since it was set, and has a value that is not null and matches
the pattern /^[a-zA-Z]*[0-9]*$/, the increment is done as a
string, preserving each character within its range, with carry:
print ++($foo = '99'); # prints '100'
print ++($foo = 'a0'); # prints 'a1'
print ++($foo = 'Az'); # prints 'Ba'
print ++($foo = 'zz'); # prints 'aaa'
The autodecrement is not magical.
The range operator (in an array context) makes use of the magical
autoincrement algorithm if the minimum and maximum are strings.
You can say
@alphabet = ('A' .. 'Z');
to get all the letters of the alphabet, or
$hexdigit = (0 .. 9, 'a' .. 'f')[$num & 15];
to get a hexadecimal digit, or
@z2 = ('01' .. '31'); print @z2[$mday];
to get dates with leading zeros. (If the final value specified
is not in the sequence that the magical increment would produce,
the sequence goes until the next value would be longer than the
final value specified.)
The || and && operators differ from C's in that, rather than
returning 0 or 1, they return the last value evaluated. Thus, a
portable way to find out the home directory might be:
$home = $ENV{'HOME'} || $ENV{'LOGDIR'} ||
(getpwuid($<))[7] || die "You're homeless!\n";
æKY Perl…Operators
æC
Along with the literals and variables mentioned earlier, the
operations in the following section can serve as terms in an
expression. Some of these operations take a LIST as an argument.
Such a list can consist of any combination of scalar arguments or
array values; the array values will be included in the list as if
each individual element were interpolated at that point in the
list, forming a longer single-dimensional array value. Elements
of the LIST should be separated by commas. If an operation is
listed both with and without parentheses around its arguments, it
means you can either use it as a unary operator or as a function
call. To use it as a function call, the next token on the same
line must be a left parenthesis. (There may be intervening white
space.) Such a function then has highest precedence, as you would
expect from a function. If any token other than a left parenthesis
follows, then it is a unary operator, with a pre cedence depending
only on whether it is a LIST operator or not. LIST operators have
lowest precedence. All other unary operators have a precedence
greater than relational operators but less than arithmetic operators.
See the section on Precedence.
For operators that can be used in either a scalar or array context,
failure is generally indicated in a scalar context by returning the
undefined value, and in an array context by returning the null list.
Remember though that THERE IS NO GENERAL RULE FOR CONVERTING A LIST
INTO A SCALAR. Each operator decides which sort of scalar it would
be most appropriate to return. Some operators return the length of
the list that would have been returned in an array context. Some
operators return the first value in the list. Some operators return
the last value in the list. Some operators return a count of
successful operations. In general, they do what you want, unless
you want consistency.
æKL accept
alarm
atan2
bind
binmode
caller
chdir
chmod
chop
chown
chroot
close
closedir
connect
cos
crypt
dbmclose
dbmopen
defined
delete
die
do
do
do
dump
each
eof
eval
exec
exit
exp
fcntl
fileno
flock
fork
getc
getlogin
getpeername
getpgrp
getppid
getpwnam
getsockname
getsockopt
gmtime
goto
grep
hex
index
int
ioctl
join
keys
kill
last
length
link
listen
local
localtime
log
lstat
m
mkdir
msgctl
msgget
msgsnd
msgrcv
next
oct
open
opendir
ord
pack
pipe
pop
print
printf
push
q
rand
read
readdir
readlink
recv
redo
rename
require
reset
return
reverse
rewinddir
rindex
rmdir
s
scalar
seek
seekdir
select
select
semctl
semget
semop
send
setpgrp
setpriority
setsockopt
shift
shmctl
shmget
shmread
shutdown
sin
sleep
socket
socketpair
sort
splice
split
sprintf
sqrt
srand
stat
study
substr
symlink
syscall
sysread
system
syswrite
tell
telldir
time
times
tr
truncate
umask
undef
unlink
unpack
unshift
utime
values
vec
wait
waitpid
wantarray
warn
write
æKY accept
æDT accept(NEWSOCKET,GENERICSOCKET)
æC accept(NEWSOCKET,GENERICSOCKET)
Does the same thing that the accept system call does.
Returns true if it succeeded, false otherwise. See exam-
ple in section on Interprocess Communication.
æKY alarm
æDT alarm(SECONDS)
æC alarm(SECONDS)
alarm SECONDS
Arranges to have a SIGALRM delivered to this process
after the specified number of seconds (minus 1, actually)
have elapsed. Thus, alarm(15) will cause a SIGALRM at
some point more than 14 seconds in the future. Only one
timer may be counting at once. Each call disables the
previous timer, and an argument of 0 may be supplied to
cancel the previous timer without starting a new one.
The returned value is the amount of time remaining on the
previous timer.
æKY atan2
æDT atan2(Y,X)
æC atan2(Y,X)
Returns the arctangent of Y/X in the range -PI to PI.
æKY bind
æDT bind(SOCKET,NAME)
æC bind(SOCKET,NAME)
Does the same thing that the bind system call does.
Returns true if it succeeded, false otherwise. NAME
should be a packed address of the proper type for the
socket. See example in section on Interprocess
Communication.
æKY binmode
æDT binmode(FILEHANDLE)
æC binmode(FILEHANDLE)
binmode FILEHANDLE
Arranges for the file to be read in "binary" mode in
operating systems that distinguish between binary and
text files. Files that are not read in binary mode have
CR LF sequences translated to LF on input and LF
translated to CR LF on output. Binmode has no effect
under Unix. If FILEHANDLE is an expression, the value is
taken as the name of the filehandle.
æKY caller
æDT caller(EXPR)
æC caller(EXPR)
caller
Returns the context of the current subroutine call:
($package,$filename,$line) = caller;
With EXPR, returns some extra information that the
debugger uses to print a stack trace. The value of EXPR
indicates how many call frames to go back before the
current one.
æKY chdir
æDT chdir(EXPR)
æC chdir(EXPR)
chdir EXPR
Changes the working directory to EXPR, if possible. If
EXPR is omitted, changes to home directory. Returns 1
upon success, 0 otherwise. See example under die.
æKY chmod
æDT chmod(LIST)
æC chmod(LIST)
chmod LIST
Changes the permissions of a list of files. The first
element of the list must be the numerical mode. Returns
the number of files successfully changed.
$cnt = chmod 0755, 'foo', 'bar';
chmod 0755, @executables;
æKY chop
æDT chop(LIST)
æC chop(LIST)
chop(VARIABLE)
chop VARIABLE
chop
Chops off the last character of a string and returns the
character chopped. It's used primarily to remove the
newline from the end of an input record, but is much more
efficient than s/\n// because it neither scans nor copies
the string. If VARIABLE is omitted, chops $_. Example:
while (<>) {
chop; # avoid \n on last field
@array = split(/:/);
...
}
You can actually chop anything that's an lvalue, includ-
ing an assignment:
chop($cwd = `pwd`);
chop($answer = <STDIN>);
If you chop a list, each element is chopped. Only the
value of the last chop is returned.
æKY chown
æDT chown(LIST)
æC chown(LIST)
chown LIST
Changes the owner (and group) of a list of files. The
first two elements of the list must be the NUMERICAL uid
and gid, in that order. Returns the number of files suc-
cessfully changed.
$cnt = chown $uid, $gid, 'foo', 'bar';
chown $uid, $gid, @filenames;
Here's an example of looking up non-numeric uids in the passwd file:
print "User: ";
$user = <STDIN>;
chop($user);
print "Files: "
$pattern = <STDIN>;
chop($pattern);
open(pass, '/etc/passwd')
|| die "Can't open passwd: $!\n";
while (<pass>) {
($login,$pass,$uid,$gid) = split(/:/);
$uid{$login} = $uid;
$gid{$login} = $gid;
}
@ary = <${pattern}>; # get filenames
if ($uid{$user} eq '') {
die "$user not in passwd file";
}
else {
chown $uid{$user}, $gid{$user}, @ary;
}
æKY chroot
æDT chroot(FILENAME)
æC chroot(FILENAME)
chroot FILENAME
Does the same as the system call of that name. If you
don't know what it does, don't worry about it. If
FILENAME is omitted, does chroot to $_.
æKY close
æDT close(FILEHANDLE)
æC close(FILEHANDLE)
close FILEHANDLE
Closes the file or pipe associated with the file handle.
You don't have to close FILEHANDLE if you are immediately
going to do another open on it, since open will close it
for you. (See open.) However, an explicit close on an
input file resets the line counter ($.), while the impli-
cit close done by open does not. Also, closing a pipe
will wait for the process executing on the pipe to com-
plete, in case you want to look at the output of the pipe
afterwards. Closing a pipe explicitly also puts the
status value of the command into $?. Example:
open(OUTPUT, '|sort >foo'); # pipe to sort
... # print stuff to output
close OUTPUT; # wait for sort to finish
open(INPUT, 'foo'); # get sort's results
FILEHANDLE may be an expression whose value gives the
real filehandle name.
æKY closedir
æDT closedir(DIRHANDLE)
æC closedir(DIRHANDLE)
closedir DIRHANDLE
Closes a directory opened by opendir().
æKY connect
æDT connect(SOCKET,NAME)
æC connect(SOCKET,NAME)
Does the same thing that the connect system call does.
Returns true if it succeeded, false otherwise. NAME
should be a package address of the proper type for the
socket. See example in section on Interprocess Communi-
cation.
æKY cos
æDT cos(EXPR)
æC cos(EXPR)
cos EXPR
Returns the cosine of EXPR (expressed in radians). If
EXPR is omitted takes cosine of $_.
æKY crypt
æDT crypt(PLAINTEXT,SALT)
æC crypt(PLAINTEXT,SALT)
Encrypts a string exactly like the crypt() function in
the C library. Useful for checking the password file for
lousy passwords. Only the guys wearing white hats should
do this.
æKY dbmclose
æDT dbmclose(ASSOC_ARRAY)
æC dbmclose(ASSOC_ARRAY)
dbmclose ASSOC_ARRAY
Breaks the binding between a dbm file and an associative
array. The values remaining in the associative array are
meaningless unless you happen to want to know what was in
the cache for the dbm file. This function is only useful
if you have ndbm.
æKY dbmopen
æDT dbmopen(ASSOC,DBNAME,MODE)
æC dbmopen(ASSOC,DBNAME,MODE)
This binds a dbm or ndbm file to an associative array.
ASSOC is the name of the associative array. (Unlike nor-
mal open, the first argument is NOT a filehandle, even
though it looks like one). DBNAME is the name of the
database (without the .dir or .pag extension). If the
database does not exist, it is created with protection
specified by MODE (as modified by the umask). If your
system only supports the older dbm functions, you may
perform only one dbmopen in your program. If your system
has neither dbm nor ndbm, calling dbmopen produces a
fatal error.
Values assigned to the associative array prior to the
dbmopen are lost. A certain number of values from the
dbm file are cached in memory. By default this number is
64, but you can increase it by preallocating that number
of garbage entries in the associative array before the
dbmopen. You can flush the cache if necessary with the
reset command.
If you don't have write access to the dbm file, you can
only read associative array variables, not set them. If
you want to test whether you can write, either use file
tests or try setting a dummy array entry inside an eval,
which will trap the error.
Note that functions such as keys() and values() may
return huge array values when used on large dbm files.
You may prefer to use the each() function to iterate over
large dbm files. Example:
# print out history file offsets
dbmopen(HIST,'/usr/lib/news/history',0666);
while (($key,$val) = each %HIST) {
print $key, ' = ', unpack('L',$val), "\n";
}
dbmclose(HIST);
æKY defined
æDT defined(EXPR)
æC defined(EXPR)
defined EXPR
Returns a boolean value saying whether the lvalue EXPR
has a real value or not. Many operations return the
undefined value under exceptional conditions, such as end
of file, uninitialized variable, system error and such.
This function allows you to distinguish between an unde-
fined null string and a defined null string with opera-
tions that might return a real null string, in particular
referencing elements of an array. You may also check to
see if arrays or subroutines exist. Use on predefined
variables is not guaranteed to produce intuitive results.
Examples:
print if defined $switch{'D'};
print "$val\n" while defined($val = pop(@ary));
die "Can't readlink $sym: $!"
unless defined($value = readlink $sym);
eval '@foo = ()' if defined(@foo);
die "No XYZ package defined" unless defined %_XYZ;
sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }
See also undef.
æKY delete
æDT delete $ASSOC{KEY}
æC delete $ASSOC{KEY}
Deletes the specified value from the specified associa-
tive array. Returns the deleted value, or the undefined
value if nothing was deleted. Deleting from $ENV{} modi-
fies the environment. Deleting from an array bound to a
dbm file deletes the entry from the dbm file.
The following deletes all the values of an associative
array:
foreach $key (keys %ARRAY) {
delete $ARRAY{$key};
}
(But it would be faster to use the reset command. Saying
undef %ARRAY is faster yet.)
æKY die
æDT die(LIST)
æC die(LIST)
die LIST
Outside of an eval, prints the value of LIST to STDERR
and exits with the current value of $! (errno). If $!
is 0, exits with the value of ($? >> 8) (`command`
status). If ($? >> 8) is 0, exits with 255. Inside an
eval, the error message is stuffed into $@ and the eval
is terminated with the undefined value.
Equivalent examples:
die "Can't cd to spool: $!\n"
unless chdir '/usr/spool/news';
chdir '/usr/spool/news' || die "Can't cd to spool: $!\n"
If the value of EXPR does not end in a newline, the
current script line number and input line number (if any)
are also printed, and a newline is supplied. Hint: some-
times appending ", stopped" to your message will cause it
to make better sense when the string "at foo line 123" is
appended. Suppose you are running script "canasta".
die "/etc/games is no good";
die "/etc/games is no good, stopped";
produce, respectively
/etc/games is no good at canasta line 123.
/etc/games is no good, stopped at canasta line 123.
See also exit.
æKY do
æDT do BLOCK
æC do BLOCK
Returns the value of the last command in the sequence of
commands indicated by BLOCK. When modified by a loop
modifier, executes the BLOCK once before testing the loop
condition. (On other statements the loop modifiers test
the conditional first.)
do SUBROUTINE (LIST)
Executes a SUBROUTINE declared by a sub declaration, and
returns the value of the last expression evaluated in
SUBROUTINE. If there is no subroutine by that name, pro-
duces a fatal error. (You may use the "defined" operator
to determine if a subroutine exists.) If you pass arrays
as part of LIST you may wish to pass the length of the
array in front of each array. (See the section on sub-
routines later on.) SUBROUTINE may be a scalar variable,
in which case the name of the sub routine to execute is
taken from the variable. The parentheses are required to
avoid confusion with the "do EXPR" form.
As an alternate form, you may call a subroutine by pre-
fixing the name with an ampersand: &foo(@args). If you
aren't passing any arguments, you don't have to use
parentheses. If you omit the parentheses, no @_ array is
passed to the subroutine. The & form is also used to
specify subroutines to the defined and undef operators:
if (defined &$var) { &$var($parm); undef &$var; }
do EXPR
Uses the value of EXPR as a filename and executes the
contents of the file as a perl script. Its primary use
is to include subroutines from a perl subroutine library.
do 'stat.pl';
is just like
eval `cat stat.pl`;
except that it's more efficient, more concise, keeps
track of the current filename for error messages, and
searches all the -I libraries if the file isn't in the
current directory (see also the @INC array in Predefined
Names). It's the same, however, in that it does reparse
the file every time you call it, so if you are going to
use the file inside a loop you might prefer to use -P and
#include, at the expense of a little more startup time.
(The main problem with #include is that cpp doesn't grok
# comments--a workaround is to use ";#" for standalone
comments.) Note that the following are NOT equivalent:
do $foo; # eval a file
do $foo(); # call a subroutine
Note that inclusion of library routines is better done
with the "require" operator.
æKY dump
æDT dump LABEL
æC dump LABEL
This causes an immediate core dump. Primarily this is so
that you can use the undump program to turn your core
dump into an executable binary after having initialized
all your variables at the beginning of the program. When
the new binary is executed it will begin by executing a
"goto LABEL" (with all the restrictions that goto
suffers). Think of it as a goto with an intervening core
dump and reincarnation. If LABEL is omitted, restarts
the program from the top. WARNING: any files opened at
the time of the dump will NOT be open any more when the
program is reincarnated, with possible resulting confu-
sion on the part of perl. See also -u.
Example:
#!/usr/bin/perl
require 'getopt.pl';
require 'stat.pl';
%days = (
'Sun',1,
'Mon',2,
'Tue',3,
'Wed',4,
'Thu',5,
'Fri',6,
'Sat',7);
dump QUICKSTART if $ARGV[0] eq '-d';
QUICKSTART:
do Getopt('f');
æKY each
æDT each(ASSOC_ARRAY)
æC each(ASSOC_ARRAY)
each ASSOC_ARRAY
Returns a 2 element array consisting of the key and value
for the next value of an associative array, so that you
can iterate over it. Entries are returned in an
apparently random order. When the array is entirely
read, a null array is returned (which when assigned pro-
duces a FALSE (0) value). The next call to each() after
that will start iterating again. The iterator can be
reset only by reading all the elements from the array.
You must not modify the array while iterating over it.
There is a single iterator for each associative array,
shared by all each(), keys() and values() function calls
in the program. The following prints out your environ-
ment like the printenv program, only in a different
order:
while (($key,$value) = each %ENV) {
print "$key=$value\n";
}
See also keys() and values().
æKY eof
æDT eof(FILEHANDLE)
æC eof(FILEHANDLE)
eof()
eof
Returns 1 if the next read on FILEHANDLE will return end
of file, or if FILEHANDLE is not open. FILEHANDLE may be
an expression whose value gives the real filehandle name.
(Note that this function actually reads a character and
then ungetc's it, so it is not very useful in an interac-
tive context.) An eof without an argument returns the eof
status for the last file read. Empty parentheses () may
be used to indicate the pseudo file formed of the files
listed on the command line, i.e. eof() is reasonable to
use inside a while (<>) loop to detect the end of only
the last file. Use eof(ARGV) or eof without the
parentheses to test EACH file in a while (<>) loop.
Examples:
# insert dashes just before last line of last file
while (<>) {
if (eof()) {
print "--------------\n";
}
print;
}
# reset line numbering on each input file
while (<>) {
print "$.\t$_";
if (eof) { # Not eof().
close(ARGV);
}
}
æKY eval
æDT eval(EXPR)
æC eval(EXPR)
eval EXPR
eval BLOCK
EXPR is parsed and executed as if it were a little perl
program. It is executed in the context of the current
perl program, so that any variable settings, subroutine
or format definitions remain afterwards. The value
returned is the value of the last expression evaluated,
just as with subroutines. If there is a syntax error or
runtime error, or a die statement is executed, an unde-
fined value is returned by eval, and $@ is set to the
error message. If there was no error, $@ is guaranteed
to be a null string. If EXPR is omitted, evaluates $_.
The final semicolon, if any, may be omitted from the
expression.
Note that, since eval traps otherwise-fatal errors, it is
useful for determining whether a particular feature (such
as dbmopen or symlink) is implemented. It is also Perl's
exception trapping mechanism, where the die operator is
used to raise exceptions.
If the code to be executed doesn't vary, you may use the
eval-BLOCK form to trap run-time errors without incurring
the penalty of recompiling each time. The error, if any,
is still returned in $@.
Evaluating a single-quoted string (as EXPR) has the same
effect, except that the eval-EXPR form reports syntax errors
at run time via $@, whereas the eval-BLOCK form reports syntax
errors at compile time. The eval-EXPR form is optimized to
eval-BLOCK the first time it succeeds. (Since the replacement
side of a substitution is considered a single-quoted string
when you use the e modifier, the same optimization occurs there.)
Examples:
# make divide-by-zero non-fatal
eval { $answer = $a / $b; }; warn $@ if $@;
# optimized to same thing after first use
eval '$answer = $a / $b'; warn $@ if $@;
# a compile-time error
eval { $answer = };
# a run-time error
eval '$answer ='; # sets $@
æKY exec
æDT exec(LIST)
æC exec(LIST)
exec LIST
If there is more than one argument in LIST, or if LIST is
an array with more than one value, calls execvp() with
the arguments in LIST. If there is only one scalar argu-
ment, the argument is checked for shell metacharacters.
If there are any, the entire argument is passed to
"/bin/sh -c" for parsing. If there are none, the argu-
ment is split into words and passed directly to execvp(),
which is more efficient. Note: exec (and system) do not
flush your output buffer, so you may need to set $| to
avoid lost output. Examples:
exec '/bin/echo', 'Your arguments are: ', @ARGV;
exec "sort $outfile | uniq";
If you don't really want to execute the first argument,
but want to lie to the program you are executing about
its own name, you can specify the program you actually
want to run by assigning that to a variable and putting
the name of the variable in front of the LIST without a
comma. (This always forces interpretation of the LIST as
a multi-valued list, even if there is only a single
scalar in the list.) Example:
$shell = '/bin/csh';
exec $shell '-sh'; # pretend it's a login shell
æKY exit
æDT exit(EXPR)
æC exit(EXPR)
exit EXPR
Evaluates EXPR and exits immediately with that value.
Example:
$ans = <STDIN>;
exit 0 if $ans =~ /^[Xx]/;
See also die. If EXPR is omitted, exits with 0 status.
æKY exp
æDT exp(EXPR)
æC exp(EXPR)
exp EXPR
Returns e to the power of EXPR. If EXPR is omitted,
gives exp($_).
æKY fcntl
æDT fcntl(FILEHANDLE,FUNCTION,SCALAR)
æC fcntl(FILEHANDLE,FUNCTION,SCALAR)
Implements the fcntl(2) function. You'll probably have
to say
require "fcntl.ph"; # probably /usr/local/lib/perl/fcntl.ph
first to get the correct function definitions. If
fcntl.ph doesn't exist or doesn't have the correct defin-
itions you'll have to roll your own, based on your C
header files such as <sys/fcntl.h>. (There is a perl
script called h2ph that comes with the perl kit which may
help you in this.) Argument processing and value return
works just like ioctl below. Note that fcntl will pro-
duce a fatal error if used on a machine that doesn't
implement fcntl(2).
æKY fileno
æDT fileno(FILEHANDLE)
æC fileno(FILEHANDLE)
fileno FILEHANDLE
Returns the file descriptor for a filehandle. Useful for
constructing bitmaps for select(). If FILEHANDLE is an
expression, the value is taken as the name of the
filehandle.
æKY flock
æDT flock(FILEHANDLE,OPERATION)
æC flock(FILEHANDLE,OPERATION)
Calls flock(2) on FILEHANDLE. See manual page for
flock(2) for definition of OPERATION. Returns true for
success, false on failure. Will produce a fatal error if
used on a machine that doesn't implement flock(2).
Here's a mailbox appender for BSD systems.
$LOCK_SH = 1;
$LOCK_EX = 2;
$LOCK_NB = 4;
$LOCK_UN = 8;
sub lock {
flock(MBOX,$LOCK_EX);
# and, in case someone appended
# while we were waiting...
seek(MBOX, 0, 2);
}
sub unlock {
flock(MBOX,$LOCK_UN);
}
open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
|| die "Can't open mailbox: $!";
do lock();
print MBOX $msg,"\n\n";
do unlock();
æKY fork
æDT fork
æC fork
Does a fork() call. Returns the child pid to the parent
process and 0 to the child process. Note: unflushed
buffers remain unflushed in both processes, which means
you may need to set $| to avoid duplicate output.
æKY getc
æDT getc(FILEHANDLE)
æC getc(FILEHANDLE)
getc FILEHANDLE
getc
Returns the next character from the input file attached
to FILEHANDLE, or a null string at EOF. If FILEHANDLE is
omitted, reads from STDIN.
æKY getlogin
æDT getlogin
æC getlogin
Returns the current login from /etc/utmp, if any. If
null, use getpwuid.
$login = getlogin || (getpwuid($<))[0] || "Some-
body";
æKY getpeername
æDT getpeername(SOCKET)
æC getpeername(SOCKET)
Returns the packed sockaddr address of other end of the
SOCKET connection.
# An internet sockaddr
$sockaddr = 'S n a4 x8';
$hersockaddr = getpeername(S);
($family, $port, $heraddr) =
unpack($sockaddr,$hersockaddr);
æKY getpgrp
æDT getpgrp(PID)
æC getpgrp(PID)
getpgrp PID
Returns the current process group for the specified PID,
0 for the current process. Will produce a fatal error if
used on a machine that doesn't implement getpgrp(2). If
EXPR is omitted, returns process group of current pro-
cess.
æKY getppid
æDT getppid
æC getppid
Returns the process id of the parent process.
æKY getpriority
æDT getpriority(WHICH,WHO)
æC getpriority(WHICH,WHO)
Returns the current priority for a process, a process
group, or a user. (See getpriority(2).) Will produce a
fatal error if used on a machine that doesn't implement
getpriority(2).
æKY getpwnam
getgrnam
gethostbyname
getnetbyname
getprotobyname
getpwuid
getgrgid
getservbyname
gethostbyaddr
getnetbyaddr
getprotobynumber
getservbyport
getpwent
getgrent
gethostent
getnetent
getprotoent
getservent
setpwent
setgrent
sethostent
setnetent
setprotoent
setservent
endpwent
endgrent
endhostent
endnetent
endprotoent
endservent
æC getpwnam(NAME)
getgrnam(NAME)
gethostbyname(NAME)
getnetbyname(NAME)
getprotobyname(NAME)
getpwuid(UID)
getgrgid(GID)
getservbyname(NAME,PROTO)
gethostbyaddr(ADDR,ADDRTYPE)
getnetbyaddr(ADDR,ADDRTYPE)
getprotobynumber(NUMBER)
getservbyport(PORT,PROTO)
getpwent
getgrent
gethostent
getnetent
getprotoent
getservent
setpwent
setgrent
sethostent(STAYOPEN)
setnetent(STAYOPEN)
setprotoent(STAYOPEN)
setservent(STAYOPEN)
endpwent
endgrent
endhostent
endnetent
endprotoent
endservent
These routines perform the same functions as their coun-
terparts in the system library. Within an array context,
the return values from the various get routines are as
follows:
($name,$passwd,$uid,$gid,
$quota,$comment,$gcos,$dir,$shell) = getpw...
($name,$passwd,$gid,$members) = getgr...
($name,$aliases,$addrtype,$length,@addrs) = gethost...
($name,$aliases,$addrtype,$net) = getnet...
($name,$aliases,$proto) = getproto...
($name,$aliases,$port,$proto) = getserv...
(If the entry doesn't exist you get a null list.)
Within a scalar context, you get the name, unless the
function was a lookup by name, in which case you get the
other thing, whatever it is. (If the entry doesn't exist
you get the undefined value.)
For example:
$uid = getpwnam
$name = getpwuid
$name = getpwent
$gid = getgrnam
$name = getgrgid
$name = getgrent
etc.
The $members value returned by getgr... is a space
separated list of the login names of the members of the
group.
For the gethost.\|.\|. functions, if the h_errno variable
is supported in C, it will be returned to you via $? if
the function call fails. The @addrs value returned by a
successful call is a list of the raw addresses returned by
the corresponding system library call. In the Internet
domain, each address is four bytes long and you can unpack
it by saying something like:
($a,$b,$c,$d) = unpack('C4',$addr[0]);
æKY getsockname
æDT getsockname(SOCKET)
æC getsockname(SOCKET)
Returns the packed sockaddr address of this end of the
SOCKET connection.
# An internet sockaddr
$sockaddr = 'S n a4 x8';
$mysockaddr = getsockname(S);
($family, $port, $myaddr) =
unpack($sockaddr,$mysockaddr);
æKY getsockopt
æDT getsockopt(SOCKET,LEVEL,OPTNAME)
æC getsockopt(SOCKET,LEVEL,OPTNAME)
Returns the socket option requested, or undefined if
there is an error.
æKY gmtime
æDT gmtime(EXPR)
æC gmtime(EXPR)
gmtime EXPR
Converts a time as returned by the time function to a 9-
element array with the time analyzed for the Greenwich
timezone. Typically used as follows:
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
gmtime(time);
All array elements are numeric, and come straight out of
a struct tm. In particular this means that $mon has the
range 0..11 and $wday has the range 0..6. If EXPR is
omitted, does gmtime(time).
æKY goto
æDT goto LABEL
æC goto LABEL
Finds the statement labeled with LABEL and resumes execu-
tion there. Currently you may only go to statements in
the main body of the program that are not nested inside a
do {} construct. This statement is not implemented very
efficiently, and is here only to make the sed-to-perl
translator easier. I may change its semantics at any
time, consistent with support for translated sed scripts.
Use it at your own risk. Better yet, don't use it at
all.
æKY grep
æDT grep(EXPR,LIST)
æC grep(EXPR,LIST)
Evaluates EXPR for each element of LIST (locally setting
$_ to each element) and returns the array value consist-
ing of those elements for which the expression evaluated
to true. In a scalar context, returns the number of
times the expression was true.
@foo = grep(!/^#/, @bar); # weed out comments
Note that, since $_ is a reference into the array value,
it can be used to modify the elements of the array.
While this is useful and supported, it can cause bizarre
results if the LIST is not a named array.
æKY hex
æDT hex(EXPR)
æC hex(EXPR)
hex EXPR
Returns the decimal value of EXPR interpreted as an hex
string. (To interpret strings that might start with 0 or
0x see oct().) If EXPR is omitted, uses $_.
æKY index
æDT index(STR,SUBSTR,POSITION)
æC index(STR,SUBSTR,POSITION)
index(STR,SUBSTR)
Returns the position of the first occurrence of SUBSTR in
STR at or after POSITION. If POSITION is omitted, starts
searching from the beginning of the string. The return
value is based at 0, or whatever you've set the $[ vari-
able to. If the substring is not found, returns one less
than the base, ordinarily -1.
æKY int
æDT int(EXPR)
æC int(EXPR)
int EXPR
Returns the integer portion of EXPR. If EXPR is omitted,
uses $_.
æKY ioctl
æDT ioctl(FILEHANDLE,FUNCTION,SCALAR)
æC ioctl(FILEHANDLE,FUNCTION,SCALAR)
Implements the ioctl(2) function. You'll probably have
to say
require "ioctl.ph"; # probably /usr/local/lib/perl/ioctl.ph
first to get the correct function definitions. If
ioctl.ph doesn't exist or doesn't have the correct defin-
itions you'll have to roll your own, based on your C
header files such as <sys/ioctl.h>. (There is a perl
script called h2ph that comes with the perl kit which may
help you in this.) SCALAR will be read and/or written
depending on the FUNCTION--a pointer to the string value
of SCALAR will be passed as the third argument of the
actual ioctl call. (If SCALAR has no string value but
does have a numeric value, that value will be passed
rather than a pointer to the string value. To guarantee
this to be true, add a 0 to the scalar before using it.)
The pack() and unpack() functions are useful for manipu-
lating the values of structures used by ioctl(). The
following example sets the erase character to DEL.
require 'ioctl.ph';
$sgttyb_t = "ccccs"; # 4 chars and a short
if (ioctl(STDIN,$TIOCGETP,$sgttyb)) {
@ary = unpack($sgttyb_t,$sgttyb);
$ary[2] = 127;
$sgttyb = pack($sgttyb_t,@ary);
ioctl(STDIN,$TIOCSETP,$sgttyb)
|| die "Can't ioctl: $!";
}
The return value of ioctl (and fcntl) is as follows:
if OS returns: perl returns:
-1 undefined value
0 string "0 but true"
anything else that number
Thus perl returns true on success and false on failure,
yet you can still easily determine the actual value
returned by the operating system:
($retval = ioctl(...)) || ($retval = -1);
printf "System returned %d\n", $retval;
æKY join
æDT join(EXPR,LIST)
æC join(EXPR,LIST)
join(EXPR,ARRAY)
Joins the separate strings of LIST or ARRAY into a single
string with fields separated by the value of EXPR, and
returns the string. Example:
$_ = join(':',
$login,$passwd,$uid,$gid,$gcos,$home,$shell);
See split.
æKY keys
æDT keys(ASSOC_ARRAY)
æC keys(ASSOC_ARRAY)
keys ASSOC_ARRAY
Returns a normal array consisting of all the keys of the
named associative array. The keys are returned in an
apparently random order, but it is the same order as
either the values() or each() function produces (given
that the associative array has not been modified). Here
is yet another way to print your environment:
@keys = keys %ENV;
@values = values %ENV;
while ($#keys >= 0) {
print pop(@keys), '=', pop(@values), "\n";
}
or how about sorted by key:
foreach $key (sort(keys %ENV)) {
print $key, '=', $ENV{$key}, "\n";
}
æKY kill
æDT kill(LIST)
æC kill(LIST)
kill LIST
Sends a signal to a list of processes. The first element
of the list must be the signal to send. Returns the
number of processes successfully signaled.
$cnt = kill 1, $child1, $child2;
kill 9, @goners;
If the signal is negative, kills process groups instead
of processes. (On System V, a negative process number
will also kill process groups, but that's not portable.)
You may use a signal name in quotes.
æKY last
æDT last LABEL
æC last LABEL
last
The last command is like the break statement in C (as
used in loops); it immediately exits the loop in ques-
tion. If the LABEL is omitted, the command refers to the
innermost enclosing loop. The continue block, if any, is
not executed:
line: while (<STDIN>) {
last line if /^$/; # exit when done with header
...
}
æKY length
æDT length(EXPR)
æC length(EXPR)
length EXPR
Returns the length in characters of the value of EXPR.
If EXPR is omitted, returns length of $_.
æKY link
æDT link(OLDFILE,NEWFILE)
æC link(OLDFILE,NEWFILE)
Creates a new filename linked to the old filename.
Returns 1 for success, 0 otherwise.
æKY listen
æDT listen(SOCKET,QUEUESIZE)
æC listen(SOCKET,QUEUESIZE)
Does the same thing that the listen system call does.
Returns true if it succeeded, false otherwise. See exam-
ple in section on Interprocess Communication.
æKY local
æDT local(LIST)
æC local(LIST)
Declares the listed variables to be local to the enclos-
ing block, subroutine, eval or "do". All the listed ele-
ments must be legal lvalues. This operator works by sav-
ing the current values of those variables in LIST on a
hidden stack and restoring them upon exiting the block,
subroutine or eval. This means that called subroutines
can also reference the local variable, but not the global
one. The LIST may be assigned to if desired, which
allows you to initialize your local variables. (If no
initializer is given for a particular variable, it is
created with an undefined value.) Commonly this is used
to name the parameters to a subroutine. Examples:
sub RANGEVAL {
local($min, $max, $thunk) = @_;
local($result) = '';
local($i);
# Presumably $thunk makes reference to $i
for ($i = $min; $i < $max; $i++) {
$result .= eval $thunk;
}
$result;
}
if ($sw eq '-v') {
# init local array with global array
local(@ARGV) = @ARGV;
unshift(@ARGV,'echo');
system @ARGV;
}
# @ARGV restored
# temporarily add to digits associative array
if ($base12) {
# (NOTE: not claiming this is efficient!)
local(%digits) = (%digits,'t',10,'e',11);
do parse_num();
}
Note that local() is a run-time command, and so gets exe-
cuted every time through a loop, using up more stack
storage each time until it's all released at once when
the loop is exited.
æKY localtime
æDT localtime(EXPR)
æC localtime(EXPR)
localtime EXPR
Converts a time as returned by the time function to a 9-
element array with the time analyzed for the local
timezone. Typically used as follows:
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
localtime(time);
All array elements are numeric, and come straight out of
a struct tm. In particular this means that $mon has the
range 0..11 and $wday has the range 0..6. If EXPR is
omitted, does localtime(time).
æKY log
æDT log(EXPR)
æC log(EXPR)
log EXPR
Returns logarithm (base e) of EXPR. If EXPR is omitted,
returns log of $_.
æKY lstat
æDT lstat(FILEHANDLE)
æC lstat(FILEHANDLE)
lstat FILEHANDLE
lstat(EXPR)
lstat SCALARVARIABLE
Does the same thing as the stat() function, but stats a
symbolic link instead of the file the symbolic link
points to. If symbolic links are unimplemented on your
system, a normal stat is done.
æKY m
æDT m/PATTERN/gio
æC m/PATTERN/gio
/PATTERN/gio
Searches a string for a pattern match, and returns true
(1) or false (''). If no string is specified via the =~
or !~ operator, the $_ string is searched. (The string
specified with =~ need not be an lvalue--it may be the
result of an expression evaluation, but remember the =~
binds rather tightly.) See also the section on regular
expressions.
If / is the delimiter then the initial 'm' is optional.
With the 'm' you can use any pair of non-alphanumeric
characters as delimiters. This is particularly useful
for matching Unix path names that contain '/'. If the
final delimiter is followed by the optional letter 'i',
the matching is done in a case-insensitive manner. PAT-
TERN may contain references to scalar variables, which
will be interpolated (and the pattern recompiled) every
time the pattern search is evaluated. (Note that $) and
$| may not be interpolated because they look like end-
of-string tests.) If you want such a pattern to be com-
piled only once, add an "o" after the trailing delimiter.
This avoids expensive run-time recompilations, and is
useful when the value you are interpolating won't change
over the life of the script. If the PATTERN evaluates to
a null string, the most recent successful regular expres-
sion is used instead.
If used in a context that requires an array value, a pat-
tern match returns an array consisting of the subexpres-
sions matched by the parentheses in the pattern, i.e.
($1, $2, $3...). It does NOT actually set $1, $2, etc.
in this case, nor does it set $+, $`, $& or $'. If the
match fails, a null array is returned. If the match
succeeds, but there were no parentheses, an array value
of (1) is returned.
Examples:
open(tty, '/dev/tty');
<tty> =~ /^y/i && do foo(); # do foo if desired
if (/Version: *([0-9.]*)/) { $version = $1; }
next if m#^/usr/spool/uucp#;
# poor man's grep
$arg = shift;
while (<>) {
print if /$arg/o; # compile only once
}
if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/))
This last example splits $foo into the first two words
and the remainder of the line, and assigns those three
fields to $F1, $F2 and $Etc. The conditional is true if
any variables were assigned, i.e. if the pattern matched.
The g modifier specifies global pattern matching — that is,
matching as many times as possible within the string. How
it behaves depends on the context. In an array context, it
returns a list of all the substrings matched by all the
parentheses in the regular expression. If there are no
parentheses, it returns a list of all the matched strings,
as if there were parentheses around the whole pattern. In
a scalar context, it iterates through the string, returning
TRUE each time it matches, and FALSE when it eventually runs
out of matches. (In other words, it remembers where it left
off last time and restarts the search at that point.) It
presumes that you have not modified the string since the last
match. Modifying the string between matches may result in
undefined behavior. (You can actually get away with in-place
modifications via substr() that do not change the length of
the entire string. In general, however, you should be using
s///g for such modifications.) Examples:
# array context
($one,$five,$fifteen) = (\`uptime\` =~ /(\ed+\e.\ed+)/g);
# scalar context
$/ = ""; $* = 1;
while ($paragraph = <>) {
while ($paragraph =~ /[a-z][\'")]*[.!?]+[\'")]*\es/g) {
$sentences++;
}
}
print "$sentences\en";
?PATTERN?
This is just like the /pattern/ search, except that it
matches only once between calls to the reset operator.
This is a useful optimization when you only want to see
the first occurrence of something in each file of a set
of files, for instance. Only ?? patterns local to the
current package are reset.
æKY mkdir
æDT mkdir(FILENAME,MODE)
æC mkdir(FILENAME,MODE)
Creates the directory specified by FILENAME, with permis-
sions specified by MODE (as modified by umask). If it
succeeds it returns 1, otherwise it returns 0 and sets $!
(errno).
æKY msgctl
æDT msgctl(ID,CMD,ARG)
æC msgctl(ID,CMD,ARG)
Calls the System V IPC function msgctl. If CMD is
&IPC_STAT, then ARG must be a variable which will hold
the returned msqid_ds structure. Returns like ioctl: the
undefined value for error, "0 but true" for zero, or the
actual return value otherwise.
æKY msgget
æDT msgget(KEY,FLAGS)
æC msgget(KEY,FLAGS)
Calls the System V IPC function msgget. Returns the mes-
sage queue id, or the undefined value if there is an
error.
æKY msgsnd
æDT msgsnd(ID,MSG,FLAGS)
æC msgsnd(ID,MSG,FLAGS)
Calls the System V IPC function msgsnd to send the mes-
sage MSG to the message queue ID. MSG must begin with
the long integer message type, which may be created with
pack("L", $type). Returns true if successful, or false
if there is an error.
æKY msgrcv
æDT msgrcv(ID,VAR,SIZE,TYPE,FLAGS)
æC msgrcv(ID,VAR,SIZE,TYPE,FLAGS)
Calls the System V IPC function msgrcv to receive a mes-
sage from message queue ID into variable VAR with a max-
imum message size of SIZE. Note that if a message is
received, the message type will be the first thing in
VAR, and the maximum length of VAR is SIZE plus the size
of the message type. Returns true if successful, or
false if there is an error.
æKY next
æDT next LABEL
æC next LABEL
next
The next command is like the continue statement in C; it
starts the next iteration of the loop:
line: while (<STDIN>) {
next line if /^#/; # discard comments
...
}
Note that if there were a continue block on the above, it
would get executed even on discarded lines. If the LABEL
is omitted, the command refers to the innermost enclosing
loop.
æKY oct
æDT oct(EXPR)
æC oct(EXPR)
oct EXPR
Returns the decimal value of EXPR interpreted as an octal
string. (If EXPR happens to start off with 0x, inter-
prets it as a hex string instead.) The following will
handle decimal, octal and hex in the standard notation:
$val = oct($val) if $val =~ /^0/;
If EXPR is omitted, uses $_.
æKY open
æDT open(FILEHANDLE,EXPR)
æC open(FILEHANDLE,EXPR)
open(FILEHANDLE)
open FILEHANDLE
Opens the file whose filename is given by EXPR, and asso-
ciates it with FILEHANDLE. If FILEHANDLE is an expres-
sion, its value is used as the name of the real filehan-
dle wanted. If EXPR is omitted, the scalar variable of
the same name as the FILEHANDLE contains the filename.
If the filename begins with "<" or nothing, the file is
opened for input. If the filename begins with ">", the
file is opened for output. If the filename begins with
">>", the file is opened for appending. (You can put a
'+' in front of the '>' or '<' to indicate that you want
both read and write access to the file.) If the filename
begins with "|", the filename is interpreted as a command
to which output is to be piped, and if the filename ends
with a "|", the filename is interpreted as command which
pipes input to us. (You may not have a command that
pipes both in and out.) Opening '-' opens STDIN and open-
ing '>-' opens STDOUT. Open returns non-zero upon suc-
cess, the undefined value otherwise. If the open
involved a pipe, the return value happens to be the pid
of the subprocess. Examples:
$article = 100;
open article || die "Can't find article $article: $!\n";
while (<article>) {...
open(LOG, '>>/usr/spool/news/twitlog');
# (log is reserved)
open(article, "caesar <$article |");
# decrypt article
open(extract, "|sort >/tmp/Tmp$$");
# $$ is our process#
# process argument list of files along with any includes
foreach $file (@ARGV) {
do process($file, 'fh00'); # no pun intended
}
sub process {
local($filename, $input) = @_;
$input++; # this is a string increment
unless (open($input, $filename)) {
print STDERR "Can't open $filename: $!\n";
return;
}
while (<$input>) { # note use of indirection
if (/^#include "(.*)"/) {
do process($1, $input);
next;
}
... # whatever
}
}
You may also, in the Bourne shell tradition, specify an
EXPR beginning with ">&", in which case the rest of the
string is interpreted as the name of a filehandle (or
file descriptor, if numeric) which is to be duped and
opened. You may use & after >, >>, <, +>, +>> and +<.
The mode you specify should match the mode of the origi-
nal filehandle. Here is a script that saves, redirects,
and restores STDOUT and STDERR:
#!/usr/bin/perl
open(SAVEOUT, ">&STDOUT");
open(SAVEERR, ">&STDERR");
open(STDOUT, ">foo.out") || die "Can't redirect stdout";
open(STDERR, ">&STDOUT") || die "Can't dup stdout";
select(STDERR); $| = 1; # make unbuffered
select(STDOUT); $| = 1; # make unbuffered
print STDOUT "stdout 1\n"; # this works for
print STDERR "stderr 1\n"; # subprocesses too
close(STDOUT);
close(STDERR);
open(STDOUT, ">&SAVEOUT");
open(STDERR, ">&SAVEERR");
print STDOUT "stdout 2\n";
print STDERR "stderr 2\n";
If you open a pipe on the command "-", i.e. either "|-"
or "-|", then there is an implicit fork done, and the
return value of open is the pid of the child within the
parent process, and 0 within the child process. (Use
defined($pid) to determine if the open was successful.)
The filehandle behaves normally for the parent, but i/o
to that filehandle is piped from/to the STDOUT/STDIN of
the child process. In the child process the filehandle
isn't opened--i/o happens from/to the new STDOUT or
STDIN. Typically this is used like the normal piped open
when you want to exercise more control over just how the
pipe command gets executed, such as when you are running
setuid, and don't want to have to scan shell commands for
metacharacters. The following pairs are more or less
equivalent:
open(FOO, "|tr '[a-z]' '[A-Z]'");
open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]';
open(FOO, "cat -n '$file'|");
open(FOO, "-|") || exec 'cat', '-n', $file;
Explicitly closing any piped filehandle causes the parent
process to wait for the child to finish, and returns the
status value in $?. Note: on any operation which may do
a fork, unflushed buffers remain unflushed in both
processes, which means you may need to set $| to avoid
duplicate output.
The filename that is passed to open will have leading and
trailing whitespace deleted. In order to open a file
with arbitrary weird characters in it, it's necessary to
protect any leading and trailing whitespace thusly:
$file =~ s#^(\s)#./$1#;
open(FOO, "< $file\0");
æKY opendir
æDT opendir(DIRHANDLE,EXPR)
æC opendir(DIRHANDLE,EXPR)
Opens a directory named EXPR for processing by readdir(),
telldir(), seekdir(), rewinddir() and closedir().
Returns true if successful. DIRHANDLEs have their own
namespace separate from FILEHANDLEs.
æKY ord
æDT ord(EXPR)
æC ord(EXPR)
ord EXPR
Returns the numeric ascii value of the first character of
EXPR. If EXPR is omitted, uses $_.
æKY pack
æDT pack(TEMPLATE,LIST)
æC pack(TEMPLATE,LIST)
Takes an array or list of values and packs it into a
binary structure, returning the string containing the
structure. The TEMPLATE is a sequence of characters that
give the order and type of values, as follows:
A An ascii string, will be space padded.
a An ascii string, will be null padded.
c A signed char value.
C An unsigned char value.
s A signed short value.
S An unsigned short value.
i A signed integer value.
I An unsigned integer value.
l A signed long value.
L An unsigned long value.
n A short in "network" order.
N A long in "network" order.
v A short in VAX (little-endian) order.
V A long in VAX (little-endian) order.
f A single-precision float in the native format.
d A double-precision float in the native format.
p A pointer to a string.
x A null byte.
X Back up a byte.
@ Null fill to absolute position.
u A uuencoded string.
b A bit string (ascending bit order, like vec()).
B A bit string (descending bit order).
h A hex string (low nybble first).
H A hex string (high nybble first).
Each letter may optionally be followed by a number which
gives a repeat count. With all types except "a", "A",
"b", "B", "h" and "H", the pack function will gobble up
that many values from the LIST. A * for the repeat count
means to use however many items are left. The "a" and
"A" types gobble just one value, but pack it as a string
of length count, padding with nulls or spaces as neces-
sary. (When unpacking, "A" strips trailing spaces and
nulls, but "a" does not.) Likewise, the "b" and "B"
fields pack a string that many bits long. The "h" and
"H" fields pack a string that many nybbles long. Real
numbers (floats and doubles) are in the native machine
format only; due to the multiplicity of floating formats
around, and the lack of a standard "network" representa-
tion, no facility for interchange has been made. This
means that packed floating point data written on one
machine may not be readable on another - even if both use
IEEE floating point arithmetic (as the endian-ness of the
memory representation is not part of the IEEE spec).
Note that perl uses doubles internally for all numeric
calculation, and converting from double -> float -> dou-
ble will lose precision (i.e. unpack("f", pack("f",
$foo)) will not in general equal $foo).
Examples:
$foo = pack("cccc",65,66,67,68);
# foo eq "ABCD"
$foo = pack("c4",65,66,67,68);
# same thing
$foo = pack("ccxxcc",65,66,67,68);
# foo eq "AB\0\0CD"
$foo = pack("s2",1,2);
# "\1\0\2\0" on little-endian
# "\0\1\0\2" on big-endian
$foo = pack("a4","abcd","x","y","z");
# "abcd"
$foo = pack("aaaa","abcd","x","y","z");
# "axyz"
$foo = pack("a14","abcdefg");
# "abcdefg\0\0\0\0\0\0\0"
$foo = pack("i9pl", gmtime);
# a real struct tm (on my system anyway)
sub bintodec {
unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
}
The same template may generally also be used in the
unpack function.
æKY pipe
æDT pipe(READHANDLE,WRITEHANDLE)
æC pipe(READHANDLE,WRITEHANDLE)
Opens a pair of connected pipes like the corresponding
system call. Note that if you set up a loop of piped
processes, deadlock can occur unless you are very care-
ful. In addition, note that perl's pipes use stdio
buffering, so you may need to set $| to flush your WRI-
TEHANDLE after each command, depending on the applica-
tion. [Requires version 3.0 patchlevel 9.]
æKY pop
æDT pop(ARRAY)
æC pop(ARRAY)
pop ARRAY
Pops and returns the last value of the array, shortening
the array by 1. Has the same effect as
$tmp = $ARRAY[$#ARRAY--];
If there are no elements in the array, returns the unde-
fined value.
æKY print
æDT print(FILEHANDLE LIST)
æC print(FILEHANDLE LIST)
print(LIST)
print FILEHANDLE LIST
print LIST
print
Prints a string or a comma-separated list of strings.
Returns non-zero if successful. FILEHANDLE may be a
scalar variable name, in which case the variable contains
the name of the filehandle, thus introducing one level of
indirection. (NOTE: If FILEHANDLE is a variable and the
next token is a term, it may be misinterpreted as an
operator unless you interpose a + or put parens around
the arguments.) If FILEHANDLE is omitted, prints by
default to standard output (or to the last selected out-
put channel--see select()). If LIST is also omitted,
prints $_ to STDOUT. To set the default output channel
to something other than STDOUT use the select operation.
Note that, because print takes a LIST, anything in the
LIST is evaluated in an array context, and any subroutine
that you call will have one or more of its expressions
evaluated in an array context. Also be careful not to
follow the print keyword with a left parenthesis unless
you want the corresponding right parenthesis to terminate
the arguments to the print--interpose a + or put parens
around all the arguments.
æKY printf
æDT printf(FILEHANDLE LIST)
æC printf(FILEHANDLE LIST)
printf(LIST)
printf FILEHANDLE LIST
printf LIST
Equivalent to a "print FILEHANDLE sprintf(LIST)".
æKY push
æDT push(ARRAY,LIST)
æC push(ARRAY,LIST)
Treats ARRAY (@ is optional) as a stack, and pushes the
values of LIST onto the end of ARRAY. The length of
ARRAY increases by the length of LIST. Has the same
effect as
for $value (LIST) {
$ARRAY[++$#ARRAY] = $value;
}
but is more efficient.
æKY q
æDT q/STRING/
æC q/STRING/
qq/STRING/
qx/STRING/
These are not really functions, but simply syntactic
sugar to let you avoid putting too many backslashes into
quoted strings. The q operator is a generalized single
quote, and the qq operator a generalized double quote.
The qx operator is a generalized backquote. Any non-
alphanumeric delimiter can be used in place of /, includ-
ing newline. If the delimiter is an opening bracket or
parenthesis, the final delimiter will be the correspond-
ing closing bracket or parenthesis. (Embedded
occurrences of the closing bracket need to be backslashed
as usual.) Examples:
$foo = q!I said, "You said, 'She said it.'"!;
$bar = q('This is it.');
$today = qx{ date };
$_ .= qq
*** The previous line contains the naughty word "$&".\n
if /(ibm|apple|awk)/; # :-)
æKY rand
æDT rand(EXPR)
æC rand(EXPR)
rand EXPR
rand
Returns a random fractional number between 0 and the
value of EXPR. (EXPR should be positive.) If EXPR is
omitted, returns a value between 0 and 1. See also
srand().
æKY read
æDT read(FILEHANDLE,SCALAR,LENGTH,OFFSET)
æC read(FILEHANDLE,SCALAR,LENGTH,OFFSET)
read(FILEHANDLE,SCALAR,LENGTH)
Attempts to read LENGTH bytes of data into variable
SCALAR from the specified FILEHANDLE. Returns the number
of bytes actually read, or undef if there was an error.
SCALAR will be grown or shrunk to the length actually
read. An OFFSET may be specified to place the read data
at some other place than the beginning of the string.
This call is actually implemented in terms of stdio's
fread call. To get a true read system call, see sysread.
æKY readdir
æDT readdir(DIRHANDLE)
æC readdir(DIRHANDLE)
readdir DIRHANDLE
Returns the next directory entry for a directory opened
by opendir(). If used in an array context, returns all
the rest of the entries in the directory. If there are
no more entries, returns an undefined value in a scalar
context or a null list in an array context.
æKY readlink
æDT readlink(EXPR)
æC readlink(EXPR)
readlink EXPR
Returns the value of a symbolic link, if symbolic links
are implemented. If not, gives a fatal error. If there
is some system error, returns the undefined value and
sets $! (errno). If EXPR is omitted, uses $_.
æKY recv
æDT recv(SOCKET,SCALAR,LEN,FLAGS)
æC recv(SOCKET,SCALAR,LEN,FLAGS)
Receives a message on a socket. Attempts to receive
LENGTH bytes of data into variable SCALAR from the speci-
fied SOCKET filehandle. Returns the address of the
sender, or the undefined value if there's an error.
SCALAR will be grown or shrunk to the length actually
read. Takes the same flags as the system call of the
same name.
æKY redo
æDT redo LABEL
æC redo LABEL
redo
The redo command restarts the loop block without evaluat-
ing the conditional again. The continue block, if any,
is not executed. If the LABEL is omitted, the command
refers to the innermost enclosing loop. This command is
normally used by programs that want to lie to themselves
about what was just input:
# a simpleminded Pascal comment stripper
# (warning: assumes no { or } in strings)
line: while (<STDIN>) {
while (s|({.*}.*){.*}|$1 |) {}
s|{.*}| |;
if (s|{.*| |) {
$front = $_;
while (<STDIN>) {
if (/}/) { # end of comment?
s|^|$front{|;
redo line;
}
}
}
print;
}
æKY rename
æDT rename(OLDNAME,NEWNAME)
æC rename(OLDNAME,NEWNAME)
Changes the name of a file. Returns 1 for success, 0
otherwise. Will not work across filesystem boundaries.
æKY require
æDT require(EXPR)
æC require(EXPR)
require EXPR
require
Includes the library file specified by EXPR, or by $_ if
EXPR is not supplied. Has semantics similar to the fol-
lowing subroutine:
sub require {
local($filename) = @_;
return 1 if $INC{$filename};
local($realfilename,$result);
ITER: {
foreach $prefix (@INC) {
$realfilename = "$prefix/$filename";
if (-f $realfilename) {
$result = do $realfilename;
last ITER;
}
}
die "Can't find $filename in \@INC";
}
die $@ if $@;
die "$filename did not return true value" unless $result;
$INC{$filename} = $realfilename;
$result;
}
Note that the file will not be included twice under the
same specified name.
The file must return true as the last statement to
indicate successful execution of any initialization code,
so it's customary to end such a file with 1; unless you're
sure it'll return true otherwise.
æKY reset
æDT reset(EXPR)
æC reset(EXPR)
reset EXPR
reset
Generally used in a continue block at the end of a loop
to clear variables and reset ?? searches so that they
work again. The expression is interpreted as a list of
single characters (hyphens allowed for ranges). All
variables and arrays beginning with one of those letters
are reset to their pristine state. If the expression is
omitted, one-match searches (?pattern?) are reset to
match again. Only resets variables or searches in the
current package. Always returns 1. Examples:
reset 'X'; # reset all X variables
reset 'a-z'; # reset lower case variables
reset; # just reset ?? searches
Note: resetting "A-Z" is not recommended since you'll
wipe out your ARGV and ENV arrays.
The use of reset on dbm associative arrays does not
change the dbm file. (It does, however, flush any
entries cached by perl, which may be useful if you are
sharing the dbm file. Then again, maybe not.)
æKY return
æDT return LIST
æC return LIST
Returns from a subroutine with the value specified.
(Note that a subroutine can automatically return the
value of the last expression evaluated. That's the pre-
ferred method--use of an explicit return is a bit
slower.)
æKY reverse
æDT reverse(LIST)
æC reverse(LIST)
reverse LIST
In an array context, returns an array value consisting of
the elements of LIST in the opposite order. In a scalar
context, returns a string value consisting of the bytes
of the first element of LIST in the opposite order.
æKY rewinddir
æDT rewinddir(DIRHANDLE)
æC rewinddir(DIRHANDLE)
rewinddir DIRHANDLE
Sets the current position to the beginning of the direc-
tory for the readdir() routine on DIRHANDLE.
æKY rindex
æDT rindex(STR,SUBSTR,POSITION)
æC rindex(STR,SUBSTR,POSITION)
rindex(STR,SUBSTR)
Works just like index except that it returns the position
of the LAST occurrence of SUBSTR in STR. If POSITION is
specified, returns the last occurrence at or before that
position.
æKY rmdir
æDT rmdir(FILENAME)
æC rmdir(FILENAME)
rmdir FILENAME
Deletes the directory specified by FILENAME if it is
empty. If it succeeds it returns 1, otherwise it returns
0 and sets $! (errno). If FILENAME is omitted, uses $_.
æKY s
æDT s/PATTERN/REPLACEMENT/gieo
æC s/PATTERN/REPLACEMENT/gieo
Searches a string for a pattern, and if found, replaces
that pattern with the replacement text and returns the
number of substitutions made. Otherwise it returns false
(0). The "g" is optional, and if present, indicates that
all occurrences of the pattern are to be replaced. The
"i" is also optional, and if present, indicates that
matching is to be done in a case-insensitive manner. The
"e" is likewise optional, and if present, indicates that
the replacement string is to be evaluated as an expres-
sion rather than just as a double-quoted string. Any
non-alphanumeric delimiter may replace the slashes; if
single quotes are used, no interpretation is done on the
replacement string (the e modifier overrides this, how-
ever); if backquotes are used, the replacement string is
a command to execute whose output will be used as the
actual replacement text. If the PATTERN is delimited by
bracketing quotes, the REPLACEMENT has its own pair of
quotes, which may or may not be bracketing quotes, e.g.
s(foo)(bar) or s<foo>/bar/. If no string is specified via
the =~ or !~ operator, the $_ string is searched and
modified. (The string specified with =~ must be a scalar
variable, an array element, or an assignment to one of
those, i.e. an lvalue.) If the pattern contains a $ that
looks like a variable rather than an end-of-string test,
the variable will be interpolated into the pattern at
run-time. If you only want the pattern compiled once the
first time the variable is interpolated, add an "o" at
the end. If the PATTERN evaluates to a null string, the
most recent successful regular expression is used
instead. See also the section on regular expressions.
Examples:
s/\bgreen\b/mauve/g; # don't change wintergreen
$path =~ s|/usr/bin|/usr/local/bin|;
s/Login: $foo/Login: $bar/; # run-time pattern
($foo = $bar) =~ s/bar/foo/;
$_ = 'abc123xyz';
s/\d+/$&*2/e; # yields 'abc246xyz'
s/\d+/sprintf("%5d",$&)/e; # yields 'abc 246xyz'
s/\w/$& x 2/eg; # yields 'aabbcc 224466xxyyzz'
s/([^ ]*) *([^ ]*)/$2 $1/; # reverse 1st two fields
(Note the use of $ instead of \ in the last example. See
section on regular expressions.)
æKY scalar
æDT scalar(EXPR)
æC scalar(EXPR)
Forces EXPR to be interpreted in a scalar context and
returns the value of EXPR.
æKY seek
æDT seek(FILEHANDLE,POSITION,WHENCE)
æC seek(FILEHANDLE,POSITION,WHENCE)
Randomly positions the file pointer for FILEHANDLE, just
like the fseek() call of stdio. FILEHANDLE may be an
expression whose value gives the name of the filehandle.
Returns 1 upon success, 0 otherwise.
æKY seekdir
æDT seekdir(DIRHANDLE,POS)
æC seekdir(DIRHANDLE,POS)
Sets the current position for the readdir() routine on
DIRHANDLE. POS must be a value returned by telldir().
Has the same caveats about possible directory compaction
as the corresponding system library routine.
æKY select
æDT select(FILEHANDLE)
æC select(FILEHANDLE)
select
Returns the currently selected filehandle. Sets the
current default filehandle for output, if FILEHANDLE is
supplied. This has two effects: first, a write or a
print without a filehandle will default to this FILEHAN-
DLE. Second, references to variables related to output
will refer to this output channel. For example, if you
have to set the top of form format for more than one out-
put channel, you might do the following:
select(REPORT1);
$^ = 'report1_top';
select(REPORT2);
$^ = 'report2_top';
FILEHANDLE may be an expression whose value gives the
name of the actual filehandle. Thus:
$oldfh = select(STDERR); $| = 1; select($oldfh);
select(RBITS,WBITS,EBITS,TIMEOUT)
This calls the select system call with the bitmasks
specified, which can be constructed using fileno() and
vec(), along these lines:
$rin = $win = $ein = '';
vec($rin,fileno(STDIN),1) = 1;
vec($win,fileno(STDOUT),1) = 1;
$ein = $rin | $win;
If you want to select on many filehandles you might wish
to write a subroutine:
sub fhbits {
local(@fhlist) = split(' ',$_[0]);
local($bits);
for (@fhlist) {
vec($bits,fileno($_),1) = 1;
}
$bits;
}
$rin = &fhbits('STDIN TTY SOCK');
The usual idiom is:
($nfound,$timeleft) =
select($rout=$rin, $wout=$win, $eout=$ein, $timeout);
or to block until something becomes ready:
$nfound = select($rout=$rin, $wout=$win,
$eout=$ein, undef);
Any of the bitmasks can also be undef. The timeout, if
specified, is in seconds, which may be fractional. NOTE:
not all implementations are capable of returning the
$timeleft. If not, they always return $timeleft equal to
the supplied $timeout.
æKY semctl
æDT semctl(ID,SEMNUM,CMD,ARG)
æC semctl(ID,SEMNUM,CMD,ARG)
Calls the System V IPC function semctl. If CMD is
&IPC_STAT or &GETALL, then ARG must be a variable which
will hold the returned semid_ds structure or semaphore
value array. Returns like ioctl: the undefined value for
error, "0 but true" for zero, or the actual return value
otherwise.
æKY semget
æDT semget(KEY,NSEMS,SIZE,FLAGS)
æC semget(KEY,NSEMS,SIZE,FLAGS)
Calls the System V IPC function semget. Returns the
semaphore id, or the undefined value if there is an
error.
æKY semop
æDT semop(KEY,OPSTRING)
æC semop(KEY,OPSTRING)
Calls the System V IPC function semop to perform sema-
phore operations such as signaling and waiting. OPSTRING
must be a packed array of semop structures. Each semop
structure can be generated with 'pack("sss", $semnum,
$semop, $semflag)'. The number of semaphore operations
is implied by the length of OPSTRING. Returns true if
successful, or false if there is an error. As an exam-
ple, the following code waits on semaphore $semnum of
semaphore id $semid:
$semop = pack("sss", $semnum, -1, 0);
die "Semaphore trouble: $!\n" unless semop($semid, $semop);
To signal the semaphore, replace "-1" with "1".
æKY send
æDT send(SOCKET,MSG,FLAGS,TO)
æC send(SOCKET,MSG,FLAGS,TO)
send(SOCKET,MSG,FLAGS)
Sends a message on a socket. Takes the same flags as the
system call of the same name. On unconnected sockets you
must specify a destination to send TO. Returns the
number of characters sent, or the undefined value if
there is an error.
æKY setpgrp
æDT setpgrp(PID,PGRP)
æC setpgrp(PID,PGRP)
Sets the current process group for the specified PID, 0
for the current process. Will produce a fatal error if
used on a machine that doesn't implement setpgrp(2).
æKY setpriority
æDT setpriority(WHICH,WHO,PRIORITY)
æC setpriority(WHICH,WHO,PRIORITY)
Sets the current priority for a process, a process group,
or a user. (See setpriority(2).) Will produce a fatal
error if used on a machine that doesn't implement set-
priority(2).
æKY setsockopt
æDT setsockopt(SOCKET,LEVEL,OPTNAME,OPTVAL)
æC setsockopt(SOCKET,LEVEL,OPTNAME,OPTVAL)
Sets the socket option requested. Returns undefined if
there is an error. OPTVAL may be specified as undef if
you don't want to pass an argument.
æKY shift
æDT shift(ARRAY)
æC shift(ARRAY)
shift ARRAY
shift
Shifts the first value of the array off and returns it,
shortening the array by 1 and moving everything down. If
there are no elements in the array, returns the undefined
value. If ARRAY is omitted, shifts the @ARGV array in
the main program, and the @_ array in subroutines. (This
is determined lexically.) See also unshift(), push() and
pop(). Shift() and unshift() do the same thing to the
left end of an array that push() and pop() do to the
right end.
æKY shmctl
æDT shmctl(ID,CMD,ARG)
æC shmctl(ID,CMD,ARG)
Calls the System V IPC function shmctl. If CMD is
&IPC_STAT, then ARG must be a variable which will hold
the returned shmid_ds structure. Returns like ioctl: the
undefined value for error, "0 but true" for zero, or the
actual return value otherwise.
æKY shmget
æDT shmget(KEY,SIZE,FLAGS)
æC shmget(KEY,SIZE,FLAGS)
Calls the System V IPC function shmget. Returns the
shared memory segment id, or the undefined value if there
is an error.
æKY shmread
æDT shmread(ID,VAR,POS,SIZE)
æC shmread(ID,VAR,POS,SIZE)
shmwrite(ID,STRING,POS,SIZE)
Reads or writes the System V shared memory segment ID
starting at position POS for size SIZE by attaching to
it, copying in/out, and detaching from it. When reading,
VAR must be a variable which will hold the data read.
When writing, if STRING is too long, only SIZE bytes are
used; if STRING is too short, nulls are written to fill
out SIZE bytes. Return true if successful, or false if
there is an error.
æKY shutdown
æDT shutdown(SOCKET,HOW)
æC shutdown(SOCKET,HOW)
Shuts down a socket connection in the manner indicated by
HOW, which has the same interpretation as in the system
call of the same name.
æKY sin
æDT sin(EXPR)
æC sin(EXPR)
sin EXPR
Returns the sine of EXPR (expressed in radians). If EXPR
is omitted, returns sine of $_.
æKY sleep
æDT sleep(EXPR)
æC sleep(EXPR)
sleep EXPR
sleep
Causes the script to sleep for EXPR seconds, or forever
if no EXPR. May be interrupted by sending the process a
SIGALRM. Returns the number of seconds actually slept.
You probably cannot mix alarm() and sleep() calls, since
sleep() is often implemented using alarm().
æKY socket
æDT socket(SOCKET,DOMAIN,TYPE,PROTOCOL)
æC socket(SOCKET,DOMAIN,TYPE,PROTOCOL)
Opens a socket of the specified kind and attaches it to
filehandle SOCKET. DOMAIN, TYPE and PROTOCOL are speci-
fied the same as for the system call of the same name.
You may need to run h2ph on sys/socket.h to get the
proper values handy in a perl library file. Return true
if successful. See the example in the section on Inter-
process Communication.
æKY socketpair
æDT socketpair(SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL)
æC socketpair(SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL)
Creates an unnamed pair of sockets in the specified
domain, of the specified type. DOMAIN, TYPE and PROTOCOL
are specified the same as for the system call of the same
name. If unimplemented, yields a fatal error. Return
true if successful.
æKY sort
æDT sort(SUBROUTINE LIST)
æC sort(SUBROUTINE LIST)
sort(LIST)
sort SUBROUTINE LIST
sort LIST
Sorts the LIST and returns the sorted array value. Non-
existent values of arrays are stripped out. If SUBROUTINE
or BLOCK is omitted, sorts in standard string comparison
order. If SUBROUTINE is specified, gives the name of a
subroutine that returns an integer less than, equal to,
or greater than 0, depending on how the elements of the
array are to be ordered. In the interests of efficiency
the normal calling code for subroutines is bypassed, with
the following effects: the subroutine may not be a recur-
sive subroutine, and the two elements to be compared are
passed into the subroutine not via @_ but as $a and $b
(see example below). They are passed by reference so
don't modify $a and $b. (The <=> and cmp operators are
extremely useful in such routines.) SUBROUTINE may be a
scalar variable name, in which case the value provides
the name of the subroutine to use.
In place of a SUBROUTINE name, you can provide a BLOCK as
an anonymous, in-line sort subroutine. Examples:
# sort lexically
@articles = sort @files;
# same thing, but with explicit sort routine
@articles = sort {$a cmp $b} @files;
# same thing in reversed order
@articles = sort {$b cmp $a} @files;
# sort numerically ascending
@articles = sort {$a <=> $b} @files;
# sort numerically descending
@articles = sort {$b <=> $a} @files;
# sort using explicit subroutine name
sub byage {
$age{$a} <=> $age{$b}; # presuming integers
}
@sortedclass = sort byage @class;
sub reverse { $b cmp $a; }
@harry = ('dog','cat','x','Cain','Abel');
@george = ('gone','chased','yz','Punished','Axed');
print sort @harry;
# prints AbelCaincatdogx
print sort reverse @harry;
# prints xdogcatCainAbel
print sort @george, 'to', @harry;
# prints AbelAxedCainPunishedcatchaseddoggonetoxyz
æKY splice
æDT splice(ARRAY,OFFSET,LENGTH,LIST)
æC splice(ARRAY,OFFSET,LENGTH,LIST)
splice(ARRAY,OFFSET,LENGTH)
splice(ARRAY,OFFSET)
Removes the elements designated by OFFSET and LENGTH from
an array, and replaces them with the elements of LIST, if
any. Returns the elements removed from the array. The
array grows or shrinks as necessary. If LENGTH is omit-
ted, removes everything from OFFSET onward. The follow-
ing equivalencies hold (assuming $[ == 0):
push(@a,$x,$y) splice(@a,$#a+1,0,$x,$y)
pop(@a) splice(@a,-1)
shift(@a) splice(@a,0,1)
unshift(@a,$x,$y) splice(@a,0,0,$x,$y)
$a[$x] = $y splice(@a,$x,1,$y);
Example, assuming array lengths are passed before arrays:
sub aeq { # compare two array values
local(@a) = splice(@_,0,shift);
local(@b) = splice(@_,0,shift);
return 0 unless @a == @b; # same len?
while (@a) {
return 0 if pop(@a) ne pop(@b);
}
return 1;
}
if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }
æKY split
æDT split(/PATTERN/,EXPR,LIMIT)
æC split(/PATTERN/,EXPR,LIMIT)
split(/PATTERN/,EXPR)
split(/PATTERN/)
split
Splits a string into an array of strings, and returns it.
(If not in an array context, returns the number of fields
found and splits into the @_ array. (In an array con-
text, you can force the split into @_ by using ?? as the
pattern delimiters, but it still returns the array
value.)) If EXPR is omitted, splits the $_ string. If
PATTERN is also omitted, splits on whitespace
(/[ \t\n]+/). Anything matching PATTERN is taken to be a
delimiter separating the fields. (Note that the delim-
iter may be longer than one character.) If LIMIT is
specified, splits into no more than that many fields
(though it may split into fewer). If LIMIT is unspeci-
fied, trailing null fields are stripped (which potential
users of pop() would do well to remember). A pattern
matching the null string (not to be confused with a null
pattern //, which is just one member of the set of pat-
terns matching a null string) will split the value of
EXPR into separate characters at each point it matches
that way. For example:
print join(':', split(/ */, 'hi there'));
produces the output 'h:i:t:h:e:r:e'.
The LIMIT parameter can be used to partially split a line
($login, $passwd, $remainder) = split(/:/, $_, 3);
(When assigning to a list, if LIMIT is omitted, perl sup-
plies a LIMIT one larger than the number of variables in
the list, to avoid unnecessary work. For the list above
LIMIT would have been 4 by default. In time critical
applications it behooves you not to split into more
fields than you really need.)
If the PATTERN contains parentheses, additional array
elements are created from each matching substring in the
delimiter.
split(/([,-])/,"1-10,20");
produces the array value
(1,'-',10,',',20)
The pattern /PATTERN/ may be replaced with an expression
to specify patterns that vary at runtime. (To do runtime
compilation only once, use /$variable/o.) As a special
case, specifying a space (' ') will split on white space
just as split with no arguments does, but leading white
space does NOT produce a null first field. Thus,
split(' ') can be used to emulate awk's default behavior,
whereas split(/ /) will give you as many null initial
fields as there are leading spaces.
Example:
open(passwd, '/etc/passwd');
while (<passwd>) {
($login, $passwd, $uid, $gid, $gcos, $home, $shell)
= split(/:/);
...
}
(Note that $shell above will still have a newline on it.
See chop().) See also join.
æKY sprintf
æDT sprintf(FORMAT,LIST)
æC sprintf(FORMAT,LIST)
Returns a string formatted by the usual printf conven-
tions. The * character is not supported.
æKY sqrt
æDT sqrt(EXPR)
æC sqrt(EXPR)
sqrt EXPR
Return the square root of EXPR. If EXPR is omitted,
returns square root of $_.
æKY srand
æDT srand(EXPR)
æC srand(EXPR)
srand EXPR
Sets the random number seed for the rand operator. If
EXPR is omitted, does srand(time).
æKY stat
æDT stat(FILEHANDLE)
æC stat(FILEHANDLE)
stat FILEHANDLE
stat(EXPR)
stat SCALARVARIABLE
Returns a 13-element array giving the statistics for a
file, either the file opened via FILEHANDLE, or named by
EXPR. Returns a null list if the stat fails. Typically
used as follows:
($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
$atime,$mtime,$ctime,$blksize,$blocks)
= stat($filename);
If stat is passed the special filehandle consisting of an
underline, no stat is done, but the current contents of
the stat structure from the last stat or filetest are
returned. Example:
if (-x $file && (($d) = stat(_)) && $d < 0) {
print "$file is executable NFS file\n";
}
(This only works on machines for which the device number is negative under NFS.)
æKY study
æDT study(SCALAR)
æC study(SCALAR)
study SCALAR
study
Takes extra time to study SCALAR ($_ if unspecified) in
anticipation of doing many pattern matches on the string
before it is next modified. This may or may not save
time, depending on the nature and number of patterns you
are searching on, and on the distribution of character
frequencies in the string to be searched--you probably
want to compare runtimes with and without it to see which
runs faster. Those loops which scan for many short con-
stant strings (including the constant parts of more com-
plex patterns) will benefit most. You may have only one
study active at a time--if you study a different scalar
the first is "unstudied". (The way study works is this:
a linked list of every character in the string to be
searched is made, so we know, for example, where all the
'k' characters are. From each search string, the rarest
character is selected, based on some static frequency
tables constructed from some C programs and English text.
Only those places that contain this "rarest" character
are examined.)
For example, here is a loop which inserts index producing
entries before any line containing a certain pattern:
while (<>) {
study;
print ".IX foo\n" if /\bfoo\b/;
print ".IX bar\n" if /\bbar\b/;
print ".IX blurfl\n" if /\bblurfl\b/;
...
print;
}
In searching for /\bfoo\b/, only those locations in $_
that contain 'f' will be looked at, because 'f' is rarer
than 'o'. In general, this is a big win except in patho-
logical cases. The only question is whether it saves you
more time than it took to build the linked list in the
first place.
Note that if you have to look for strings that you don't
know till runtime, you can build an entire loop as a
string and eval that to avoid recompiling all your pat-
terns all the time. Together with undefining $/ to input
entire files as one record, this can be very fast, often
faster than specialized programs like fgrep. The follow-
ing scans a list of files (@files) for a list of words
(@words), and prints out the names of those files that
contain a match:
$search = 'while (<>) { study;';
foreach $word (@words) {
$search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n";
}
$search .= "}";
@ARGV = @files;
undef $/;
eval $search; # this screams
$/ = "\n"; # put back to normal input delim
foreach $file (sort keys(%seen)) {
print $file, "\n";
}
æKY substr
æDT substr(EXPR,OFFSET,LEN)
æC substr(EXPR,OFFSET,LEN)
substr(EXPR,OFFSET)
Extracts a substring out of EXPR and returns it. First
character is at offset 0, or whatever you've set $[ to.
If OFFSET is negative, starts that far from the end of
the string. If LEN is omitted, returns everything to the
end of the string. You can use the substr() function as
an lvalue, in which case EXPR must be an lvalue. If you
assign something shorter than LEN, the string will
shrink, and if you assign something longer than LEN, the
string will grow to accommodate it. To keep the string
the same length you may need to pad or chop your value
using sprintf().
æKY symlink
æDT symlink(OLDFILE,NEWFILE)
æC symlink(OLDFILE,NEWFILE)
Creates a new filename symbolically linked to the old
filename. Returns 1 for success, 0 otherwise. On sys-
tems that don't support symbolic links, produces a fatal
error at run time. To check for that, use eval:
$symlink_exists = (eval 'symlink("","");', $@ eq '');
æKY syscall
æDT syscall(LIST)
æC syscall(LIST)
syscall LIST
Calls the system call specified as the first element of
the list, passing the remaining elements as arguments to
the system call. If unimplemented, produces a fatal
error. The arguments are interpreted as follows: if a
given argument is numeric, the argument is passed as an
int. If not, the pointer to the string value is passed.
You are responsible to make sure a string is pre-extended
long enough to receive any result that might be written
into a string. If your integer arguments are not
literals and have never been interpreted in a numeric
context, you may need to add 0 to them to force them to
look like numbers.
require 'syscall.ph'; # may need to run h2ph
syscall(&SYS_write, fileno(STDOUT), "hi there\n", 9);
æKY sysread
æDT sysread(FILEHANDLE,SCALAR,LENGTH,OFFSET)
æC sysread(FILEHANDLE,SCALAR,LENGTH,OFFSET)
sysread(FILEHANDLE,SCALAR,LENGTH)
Attempts to read LENGTH bytes of data into variable
SCALAR from the specified FILEHANDLE, using the system
call read(2). It bypasses stdio, so mixing this with
other kinds of reads may cause confusion. Returns the
number of bytes actually read, or undef if there was an
error. SCALAR will be grown or shrunk to the length
actually read. An OFFSET may be specified to place the
read data at some other place than the beginning of the
string.
æKY system
æDT system(LIST)
æC system(LIST)
system LIST
Does exactly the same thing as "exec LIST" except that a
fork is done first, and the parent process waits for the
child process to complete. Note that argument processing
varies depending on the number of arguments. The return
value is the exit status of the program as returned by
the wait() call. To get the actual exit value divide by
256. See also exec.
æKY syswrite
æDT syswrite(FILEHANDLE,SCALAR,LENGTH,OFFSET)
æC syswrite(FILEHANDLE,SCALAR,LENGTH,OFFSET)
syswrite(FILEHANDLE,SCALAR,LENGTH)
Attempts to write LENGTH bytes of data from variable
SCALAR to the specified FILEHANDLE, using the system call
write(2). It bypasses stdio, so mixing this with prints
may cause confusion. Returns the number of bytes actu-
ally written, or undef if there was an error. An OFFSET
may be specified to place the read data at some other
place than the beginning of the string.
æKY tell
æDT tell(FILEHANDLE)
æC tell(FILEHANDLE)
tell FILEHANDLE
tell
Returns the current file position for FILEHANDLE.
FILEHANDLE may be an expression whose value gives the
name of the actual filehandle. If FILEHANDLE is omitted,
assumes the file last read.
æKY telldir
æDT telldir(DIRHANDLE)
æC telldir(DIRHANDLE)
telldir DIRHANDLE
Returns the current position of the readdir() routines on
DIRHANDLE. Value may be given to seekdir() to access a
particular location in a directory. Has the same caveats
about possible directory compaction as the corresponding
system library routine.
æKY time
æDT time
æC time
Returns the number of non-leap seconds since 00:00:00
UTC, January 1, 1970. Suitable for feeding to gmtime()
and localtime().
æKY times
æDT times
æC times
Returns a four-element array giving the user and system
times, in seconds, for this process and the children of
this process.
($user,$system,$cuser,$csystem) = times;
æKY tr
æDT tr/SEARCHLIST/REPLACEMENTLIST/cds
æC tr/SEARCHLIST/REPLACEMENTLIST/cds
y/SEARCHLIST/REPLACEMENTLIST/cds
Translates all occurrences of the characters found in the
search list with the corresponding character in the
replacement list. It returns the number of characters
replaced or deleted. If no string is specified via the
=~ or !~ operator, the $_ string is translated. (The
string specified with =~ must be a scalar variable, an
array element, or an assignment to one of those, i.e. an
lvalue.) For sed devotees, y is provided as a synonym for
tr. If the SEARCHLIST is delimited by bracketing quotes,
the REPLACEMENTLIST has its own pair of quotes, which may
or may not be bracketing quotes, e.g. tr[A-Z][a-z] or
tr(+-*/)/ABCD/.
If the c modifier is specified, the SEARCHLIST character
set is complemented. If the d modifier is specified, any
characters specified by SEARCHLIST that are not found in
REPLACEMENTLIST are deleted. (Note that this is slightly
more flexible than the behavior of some tr programs,
which delete anything they find in the SEARCHLIST,
period.) If the s modifier is specified, sequences of
characters that were translated to the same character are
squashed down to 1 instance of the character.
If the d modifier was used, the REPLACEMENTLIST is always
interpreted exactly as specified. Otherwise, if the
REPLACEMENTLIST is shorter than the SEARCHLIST, the final
character is replicated till it is long enough. If the
REPLACEMENTLIST is null, the SEARCHLIST is replicated.
This latter is useful for counting characters in a class,
or for squashing character sequences in a class.
Examples:
$ARGV[1] =~ y/A-Z/a-z/; # canonicalize to lower case
$cnt = tr/*/*/; # count the stars in $_
$cnt = tr/0-9//; # count the digits in $_
tr/a-zA-Z//s; # bookkeeper -> bokeper
($HOST = $host) =~ tr/a-z/A-Z/;
y/a-zA-Z/ /cs; # change non-alphas to single space
tr/\200-\377/\0-\177/; # delete 8th bit
æKY truncate
æDT truncate(FILEHANDLE,LENGTH)
æC truncate(FILEHANDLE,LENGTH)
truncate(EXPR,LENGTH)
Truncates the file opened on FILEHANDLE, or named by
EXPR, to the specified length. Produces a fatal error if
truncate isn't implemented on your system.
æKY umask
æDT umask(EXPR)
æC umask(EXPR)
umask EXPR
umask
Sets the umask for the process and returns the old one.
If EXPR is omitted, merely returns current umask.
æKY undef
æDT undef(EXPR)
æC undef(EXPR)
undef EXPR
undef
Undefines the value of EXPR, which must be an lvalue.
Use only on a scalar value, an entire array, or a subrou-
tine name (using &). (Undef will probably not do what
you expect on most predefined variables or dbm array
values.) Always returns the undefined value. You can
omit the EXPR, in which case nothing is undefined, but
you still get an undefined value that you could, for
instance, return from a subroutine. Examples:
undef $foo;
undef $bar{'blurfl'};
undef @ary;
undef %assoc;
undef &mysub;
return (wantarray ? () : undef) if $they_blew_it;
æKY unlink
æDT unlink(LIST)
æC unlink(LIST)
unlink LIST
Deletes a list of files. Returns the number of files
successfully deleted.
$cnt = unlink 'a', 'b', 'c';
unlink @goners;
unlink <*.bak>;
Note: unlink will not delete directories unless you are
superuser and the -U flag is supplied to perl. Even if
these conditions are met, be warned that unlinking a
directory can inflict damage on your filesystem. Use
rmdir instead.
æKY unpack
æDT unpack(TEMPLATE,EXPR)
æC unpack(TEMPLATE,EXPR)
Unpack does the reverse of pack: it takes a string
representing a structure and expands it out into an array
value, returning the array value. (In a scalar context,
it merely returns the first value produced.) The TEMPLATE
has the same format as in the pack function. Here's a
subroutine that does substring:
sub substr {
local($what,$where,$howmuch) = @_;
unpack("x$where a$howmuch", $what);
}
and then there's
sub ord { unpack("c",$_[0]); }
In addition, you may prefix a field with a %<number> to
indicate that you want a <number>-bit checksum of the
items instead of the items themselves. Default is a 16-
bit checksum. For example, the following computes the
same number as the System V sum program:
while (<>) {
$checksum += unpack("%16C*", $_);
}
$checksum %= 65536;
æKY unshift
æDT unshift(ARRAY,LIST)
æC unshift(ARRAY,LIST)
Does the opposite of a shift. Or the opposite of a push,
depending on how you look at it. Prepends list to the
front of the array, and returns the number of elements in
the new array.
unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/;
æKY utime
æDT utime(LIST)
æC utime(LIST)
utime LIST
Changes the access and modification times on each file of
a list of files. The first two elements of the list must
be the NUMERICAL access and modification times, in that
order. Returns the number of files successfully changed.
The inode modification time of each file is set to the
current time. Example of a "touch" command:
#!/usr/bin/perl
$now = time;
utime $now, $now, @ARGV;
æKY values
æDT values(ASSOC_ARRAY)
æC values(ASSOC_ARRAY)
values ASSOC_ARRAY
Returns a normal array consisting of all the values of
the named associative array. The values are returned in
an apparently random order, but it is the same order as
either the keys() or each() function would produce on the
same array. See also keys() and each().
æKY vec
æDT vec(EXPR,OFFSET,BITS)
æC vec(EXPR,OFFSET,BITS)
Treats a string as a vector of unsigned integers, and
returns the value of the bitfield specified. May also be
assigned to. BITS must be a power of two from 1 to 32.
Vectors created with vec() can also be manipulated with
the logical operators |, & and ^, which will assume a bit
vector operation is desired when both operands are
strings. This interpretation is not enabled unless there
is at least one vec() in your program, to protect older
programs.
To transform a bit vector into a string or array of 0's
and 1's, use these:
$bits = unpack("b*", $vector);
@bits = split(//, unpack("b*", $vector));
If you know the exact length in bits, it can be used in
place of the *.
æKY wait
æDT wait
æC wait
Waits for a child process to terminate and returns the
pid of the deceased process, or -1 if there are no child
processes. The status is returned in $?.
æKY waitpid
æDT waitpid(PID,FLAGS)
æC waitpid(PID,FLAGS)
Waits for a particular child process to terminate and
returns the pid of the deceased process, or -1 if there
is no such child process. The status is returned in $?.
If you say
require "sys/wait.h";
...
waitpid(-1,&WNOHANG);
then you can do a non-blocking wait for any process.
Non-blocking wait is only available on machines support-
ing either the waitpid (2) or wait4 (2) system calls.
However, waiting for a particular pid with FLAGS of 0 is
implemented everywhere. (Perl emulates the system call
by remembering the status values of processes that have
exited but have not been harvested by the Perl script
yet.)
æKY wantarray
æDT wantarray
æC wantarray
Returns true if the context of the currently executing
subroutine is looking for an array value. Returns false
if the context is looking for a scalar.
return wantarray ? () : undef;
æKY warn
æDT warn(LIST)
æC warn(LIST)
warn LIST
Produces a message on STDERR just like "die", but doesn't
exit.
æKY write
æDT write(FILEHANDLE)
æC write(FILEHANDLE)
write(EXPR)
write
Writes a formatted record (possibly multi-line) to the
specified file, using the format associated with that
file. By default the format for a file is the one having
the same name is the filehandle, but the format for the
current output channel (see select) may be set explicitly
by assigning the name of the format to the $~ variable.
Top of form processing is handled automatically: if there
is insufficient room on the current page for the format-
ted record, the page is advanced by writing a form feed,
a special top-of-page format is used to format the new
page header, and then the record is written. By default
the top-of-page format is the name of the filehandle with
"_TOP" appended, but it may be dynamicallly set to the
format of your choice by assigning the name to the $^
variable while the filehandle is selected. The number of
lines remaining on the current page is in variable $-,
which can be set to 0 to force a new page.
If FILEHANDLE is unspecified, output goes to the current
default output channel, which starts out as STDOUT but
may be changed by the select operator. If the FILEHANDLE
is an EXPR, then the expression is evaluated and the
resulting string is used to look up the name of the
FILEHANDLE at run time. For more on formats, see the
section on formats later on.
Note that write is NOT the opposite of read.
æKY Perl…Precedence
æC
Perl operators have the following associativity and precedence:
nonassoc print printf exec system sort reverse
chmod chown kill unlink utime die return
left ,
right = += -= *= etc.
right ?:
nonassoc ..
left ||
left &&
left | ^
left &
nonassoc == != <=> eq ne cmp
nonassoc < > <= >= lt gt le ge
nonassoc chdir exit eval reset sleep rand umask
nonassoc -r -w -x etc.
left << >>
left + - .
left * / % x
left =~ !~
right ! ~ and unary minus
right **
nonassoc ++ --
left '('
As mentioned earlier, if any list operator (print, etc.) or any
unary operator (chdir, etc.) is followed by a left parenthesis as
the next token on the same line, the operator and arguments
within parentheses are taken to be of highest precedence, just
like a normal function call. Examples:
chdir $foo || die; # (chdir $foo) || die
chdir($foo) || die; # (chdir $foo) || die
chdir ($foo) || die; # (chdir $foo) || die
chdir +($foo) || die; # (chdir $foo) || die
but, because * is higher precedence than ||:
chdir $foo * 20; # chdir ($foo * 20)
chdir($foo) * 20; # (chdir $foo) * 20
chdir ($foo) * 20; # (chdir $foo) * 20
chdir +($foo) * 20; # chdir ($foo * 20)
rand 10 * 20; # rand (10 * 20)
rand(10) * 20; # (rand 10) * 20
rand (10) * 20; # (rand 10) * 20
rand +(10) * 20; # rand (10 * 20)
In the absence of parentheses, the precedence of list operators
such as print, sort or chmod is either very high or very low
depending on whether you look at the left side of operator or the
right side of it. For example, in
@ary = (1, 3, sort 4, 2);
print @ary; # prints 1324
the commas on the right of the sort are evaluated before the
sort, but the commas on the left are evaluated after. In other
words, list operators tend to gobble up all the arguments that
follow them, and then act like a simple term with regard to the
preceding expression. Note that you have to be careful with
parens:
# These evaluate exit before doing the print:
print($foo, exit); # Obviously not what you want.
print $foo, exit; # Nor is this.
# These do the print before evaluating exit:
(print $foo), exit; # This is what you want.
print($foo), exit; # Or this.
print ($foo), exit; # Or even this.
Also note that
print ($foo & 255) + 1, "\n";
probably doesn't do what you expect at first glance.
æKY Perl…Subroutines
æC
A subroutine may be declared as follows:
sub NAME BLOCK
Any arguments passed to the routine come in as array @_, that is
($_[0], $_[1], ...). The array @_ is a local array, but its
values are references to the actual scalar parameters. The
return value of the subroutine is the value of the last expres-
sion evaluated, and can be either an array value or a scalar
value. Alternately, a return statement may be used to specify
the returned value and exit the subroutine. To create local
variables see the local operator.
A subroutine is called using the do operator or the & operator.
Example:
sub MAX {
local($max) = pop(@_);
foreach $foo (@_) {
$max = $foo if $max < $foo;
}
$max;
}
...
$bestday = &MAX($mon,$tue,$wed,$thu,$fri);
Example:
# get a line, combining continuation lines
# that start with whitespace
sub get_line {
$thisline = $lookahead;
line: while ($lookahead = <STDIN>) {
if ($lookahead =~ /^[ \t]/) {
$thisline .= $lookahead;
}
else {
last line;
}
}
$thisline;
}
$lookahead = <STDIN>; # get first line
while ($_ = do get_line()) {
...
}
Use array assignment to a local list to name your formal arguments:
sub maybeset {
local($key, $value) = @_;
$foo{$key} = $value unless $foo{$key};
}
This also has the effect of turning call-by-reference into call-
by-value, since the assignment copies the values.
Subroutines may be called recursively. If a subroutine is called
using the & form, the argument list is optional. If omitted, no
@_ array is set up for the subroutine; the @_ array at the time
of the call is visible to subroutine instead.
do foo(1,2,3); # pass three arguments
&foo(1,2,3); # the same
do foo(); # pass a null list
&foo(); # the same
&foo; # pass no arguments--more efficient
Passing By Reference
Sometimes you don't want to pass the value of an array to a sub-
routine but rather the name of it, so that the subroutine can
modify the global copy of it rather than working with a local
copy. In perl you can refer to all the objects of a particular
name by prefixing the name with a star: *foo. When evaluated, it
produces a scalar value that represents all the objects of that
name, including any filehandle, format or subroutine. When
assigned to within a local() operation, it causes the name men-
tioned to refer to whatever * value was assigned to it. Example:
sub doubleary {
local(*someary) = @_;
foreach $elem (@someary) {
$elem *= 2;
}
}
do doubleary(*foo);
do doubleary(*bar);
Assignment to *name is currently recommended only inside a
local(). You can actually assign to *name anywhere, but the pre-
vious referent of *name may be stranded forever. This may or may
not bother you.
Note that scalars are already passed by reference, so you can
modify scalar arguments without using this mechanism by referring
explicitly to the $_[nnn] in question. You can modify all the
elements of an array by passing all the elements as scalars, but
you have to use the * mechanism to push, pop or change the size
of an array. The * mechanism will probably be more efficient in
any case.
Since a *name value contains unprintable binary data, if it is
used as an argument in a print, or as a %s argument in a printf
or sprintf, it then has the value '*name', just so it prints out
pretty.
Even if you don't want to modify an array, this mechanism is use-
ful for passing multiple arrays in a single LIST, since normally
the LIST mechanism will merge all the array values so that you
can't extract out the individual arrays.
æKY Perl…Regexp
æC
Regular Expressions
The patterns used in pattern matching are regular expressions
such as those supplied in the Version 8 regexp routines. (In
fact, the routines are derived from Henry Spencer's freely redis-
tributable reimplementation of the V8 routines.) In addition, \w
matches an alphanumeric character (including "_") and \W a nonal-
phanumeric. Word boundaries may be matched by \b, and non-
boundaries by \B. A whitespace character is matched by \s, non-
whitespace by \S. A numeric character is matched by \d, non-
numeric by \D. You may use \w, \s and \d within character
classes. Also, \n, \r, \f, \t and \NNN have their normal
interpretations. Within character classes \b represents back-
space rather than a word boundary. Alternatives may be separated
by |. The bracketing construct ( ... ) may also be used, in
which case \<digit> matches the digit'th substring. (Outside of
the pattern, always use $ instead of \ in front of the digit.
The scope of $<digit> (and $`, $& and $') extends to the end of
the enclosing BLOCK or eval string, or to the next pattern match
with subexpressions. The \<digit> notation sometimes works out-
side the current pattern, but should not be relied upon.) You may
have as many parentheses as you wish. If you have more than 9
substrings, the variables $10, $11, ... refer to the correspond-
ing substring. Within the pattern, \10, \11, etc. refer back to
substrings if there have been at least that many left parens
before the backreference. Otherwise (for backward compatibilty)
\10 is the same as \010, a backspace, and \11 the same as \011, a
tab. And so on. (\1 through \9 are always backreferences.)
$+ returns whatever the last bracket match matched. $& returns
the entire matched string. ($0 used to return the same thing,
but not any more.) $` returns everything before the matched
string. $' returns everything after the matched string. Exam-
ples:
s/^([^ ]*) *([^ ]*)/$2 $1/; # swap first two words
if (/Time: (..):(..):(..)/) {
$hours = $1;
$minutes = $2;
$seconds = $3;
}
By default, the ^ character is only guaranteed to match at the
beginning of the string, the $ character only at the end (or
before the newline at the end) and perl does certain optimiza-
tions with the assumption that the string contains only one line.
The behavior of ^ and $ on embedded newlines will be incon-
sistent. You may, however, wish to treat a string as a multi-
line buffer, such that the ^ will match after any newline within
the string, and $ will match before any newline. At the cost of
a little more overhead, you can do this by setting the variable
$* to 1. Setting it back to 0 makes perl revert to its old
behavior.
To facilitate multi-line substitutions, the . character never
matches a newline (even when $* is 0). In particular, the fol-
lowing leaves a newline on the $_ string:
$_ = <STDIN>;
s/.*(some_string).*/$1/;
If the newline is unwanted, try one of
s/.*(some_string).*\n/$1/;
s/.*(some_string)[^\000]*/$1/;
s/.*(some_string)(.|\n)*/$1/;
chop; s/.*(some_string).*/$1/;
/(some_string)/ && ($_ = $1);
Any item of a regular expression may be followed with digits in
curly brackets of the form {n,m}, where n gives the minimum
number of times to match the item and m gives the maximum. The
form {n} is equivalent to {n,n} and matches exactly n times. The
form {n,} matches n or more times. (If a curly bracket occurs in
any other context, it is treated as a regular character.) The *
modifier is equivalent to {0,}, the + modifier to {1,} and the ?
modifier to {0,1}. There is no limit to the size of n or m, but
large numbers will chew up more memory.
You will note that all backslashed metacharacters in perl are
alphanumeric, such as \b, \w, \n. Unlike some other regular
expression languages, there are no backslashed symbols that
aren't alphanumeric. So anything that looks like \\, \(, \), \<,
\>, \{, or \} is always interpreted as a literal character, not a
metacharacter. This makes it simple to quote a string that you
want to use for a pattern but that you are afraid might contain
metacharacters. Simply quote all the non-alphanumeric charac-
ters:
$pattern =~ s/(\W)/\\$1/g;
æKY Perl…Formats
æC
Output record formats for use with the write operator may
declared as follows:
format NAME =
FORMLIST
.
If name is omitted, format "STDOUT" is defined. FORMLIST con-
sists of a sequence of lines, each of which may be of one of
three types:
1. A comment.
2. A "picture" line giving the format for one output line.
3. An argument line supplying values to plug into a picture
line.
Picture lines are printed exactly as they look, except for cer-
tain fields that substitute values into the line. Each picture
field starts with either @ or ^. The @ field (not to be confused
with the array marker @) is the normal case; ^ fields are used to
do rudimentary multi-line text block filling. The length of the
field is supplied by padding out the field with multiple <, >, or
| characters to specify, respectively, left justification, right
justification, or centering. As an alternate form of right jus-
tification, you may also use # characters (with an optional .) to
specify a numeric field. (Use of ^ instead of @ causes the field
to be blanked if undefined.) If any of the values supplied for
these fields contains a newline, only the text up to the newline
is printed. The special field @* can be used for printing
multi-line values. It should appear by itself on a line.
The values are specified on the following line, in the same order
as the picture fields. The values should be separated by commas.
Picture fields that begin with ^ rather than @ are treated spe-
cially. The value supplied must be a scalar variable name which
contains a text string. Perl puts as much text as it can into
the field, and then chops off the front of the string so that the
next time the variable is referenced, more of the text can be
printed. Normally you would use a sequence of fields in a verti-
cal stack to print out a block of text. If you like, you can end
the final field with ..., which will appear in the output if the
text was too long to appear in its entirety. You can change
which characters are legal to break on by changing the variable
$: to a list of the desired characters.
Since use of ^ fields can produce variable length records if the
text to be formatted is short, you can suppress blank lines by
putting the tilde (~) character anywhere in the line. (Normally
you should put it in the front if possible, for visibility.) The
tilde will be translated to a space upon output. If you put a
second tilde contiguous to the first, the line will be repeated
until all the fields on the line are exhausted. (If you use a
field of the @ variety, the expression you supply had better not
give the same value every time forever!)
Examples:
# a report on the /etc/passwd file
format STDOUT_TOP =
Passwd File
Name Login Office Uid Gid Home
------------------------------------------------------------------
.
format STDOUT =
@<<<<<<<<<<<<<<<<<< @||||||| @<<<<<<@>>>> @>>>> @<<<<<<<<<<<<<<<<<
$name, $login, $office,$uid,$gid, $home
.
# a report from a bug report form
format STDOUT_TOP =
Bug Reports
@<<<<<<<<<<<<<<<<<<<<<<< @||| @>>>>>>>>>>>>>>>>>>>>>>>
$system, $%, $date
------------------------------------------------------------------
.
format STDOUT =
Subject: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$subject
Index: @<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$index, $description
Priority: @<<<<<<<<<< Date: @<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$priority, $date, $description
From: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$from, $description
Assigned to: @<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$programmer, $description
~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$description
~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$description
~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$description
~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$description
~ ^<<<<<<<<<<<<<<<<<<<<<<<...
$description
.
It is possible to intermix prints with writes on the same output
channel, but you'll have to handle $- (lines left on the page)
yourself.
If you are printing lots of fields that are usually blank, you
should consider using the reset operator between records. Not
only is it more efficient, but it can prevent the bug of adding
another field and forgetting to zero it.
æKY Perl…IPC
æC
The IPC facilities of perl are built on the Berkeley socket
mechanism. If you don't have sockets, you can ignore this sec-
tion. The calls have the same names as the corresponding system
calls, but the arguments tend to differ, for two reasons. First,
perl file handles work differently than C file descriptors.
Second, perl already knows the length of its strings, so you
don't need to pass that information. Here is a sample client
(untested):
($them,$port) = @ARGV;
$port = 2345 unless $port;
$them = 'localhost' unless $them;
$SIG{'INT'} = 'dokill';
sub dokill { kill 9,$child if $child; }
require 'sys/socket.ph';
$sockaddr = 'S n a4 x8';
chop($hostname = `hostname`);
($name, $aliases, $proto) = getprotobyname('tcp');
($name, $aliases, $port) = getservbyname($port, 'tcp')
unless $port =~ /^\d+$/;
($name, $aliases, $type, $len, $thisaddr) =
gethostbyname($hostname);
($name, $aliases, $type, $len, $thataddr) = gethostbyname($them);
$this = pack($sockaddr, &AF_INET, 0, $thisaddr);
$that = pack($sockaddr, &AF_INET, $port, $thataddr);
socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
bind(S, $this) || die "bind: $!";
connect(S, $that) || die "connect: $!";
select(S); $| = 1; select(stdout);
if ($child = fork) {
while (<>) {
print S;
}
sleep 3;
do dokill();
}
else {
while (<S>) {
print;
And here's a server:
($port) = @ARGV;
$port = 2345 unless $port;
require 'sys/socket.ph';
$sockaddr = 'S n a4 x8';
($name, $aliases, $proto) = getprotobyname('tcp');
($name, $aliases, $port) = getservbyname($port, 'tcp')
unless $port =~ /^\d+$/;
$this = pack($sockaddr, &AF_INET, $port, "\0\0\0\0");
select(NS); $| = 1; select(stdout);
socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
bind(S, $this) || die "bind: $!";
listen(S, 5) || die "connect: $!";
select(S); $| = 1; select(stdout);
for (;;) {
print "Listening again\n";
($addr = accept(NS,S)) || die $!;
print "accept ok\n";
($af,$port,$inetaddr) = unpack($sockaddr,$addr);
@inetaddr = unpack('C4',$inetaddr);
print "$af $port @inetaddr\n";
while (<NS>) {
print;
print NS;
}
}
æKY Perl…Variables
æC
The following names have special meaning to perl. I could have
used alphabetic symbols for some of these, but I didn't want to
take the chance that someone would say reset "a-zA-Z" and wipe
them all out. You'll just have to suffer along with these silly
symbols. Most of them have reasonable mnemonics, or analogues in
one of the shells.
$_ The default input and pattern-searching space. The fol-
lowing pairs are equivalent:
while (<>) {... # only equivalent in while!
while ($_ = <>) {...
/^Subject:/
$_ =~ /^Subject:/
y/a-z/A-Z/
$_ =~ y/a-z/A-Z/
chop
chop($_)
(Mnemonic: underline is understood in certain opera-
tions.)
$. The current input line number of the last filehandle that
was read. Readonly. Remember that only an explicit
close on the filehandle resets the line number. Since <>
never does an explicit close, line numbers increase
across ARGV files (but see examples under eof).
(Mnemonic: many programs use . to mean the current line
number.)
$/ The input record separator, newline by default. Works
like awk's RS variable, including treating blank lines as
delimiters if set to the null string. You may set it to
a multicharacter string to match a multi-character delim-
iter. Note that setting it to "\n\n" means something
slightly different than setting it to "", if the file
contains consecutive blank lines. Setting it to "" will
treat two or more consecutive blank lines as a single
blank line. Setting it to "\n\n" will blindly assume that
the next input character belongs to the next paragraph,
even if it's a newline. (Mnemonic: / is used to delimit
line boundaries when quoting poetry.)
$, The output field separator for the print operator. Ordi-
narily the print operator simply prints out the comma
separated fields you specify. In order to get behavior
more like awk, set this variable as you would set awk's
OFS variable to specify what is printed between fields.
(Mnemonic: what is printed when there is a , in your
print statement.)
$" This is like $, except that it applies to array values
interpolated into a double-quoted string (or similar
interpreted string). Default is a space. (Mnemonic:
obvious, I think.)
$\ The output record separator for the print operator.
Ordinarily the print operator simply prints out the comma
separated fields you specify, with no trailing newline or
record separator assumed. In order to get behavior more
like awk, set this variable as you would set awk's ORS
variable to specify what is printed at the end of the
print. (Mnemonic: you set $\ instead of adding \n at the
end of the print. Also, it's just like /, but it's what
you get "back" from perl.)
$# The output format for printed numbers. This variable is
a half-hearted attempt to emulate awk's OFMT variable.
There are times, however, when awk and perl have differ-
ing notions of what is in fact numeric. Also, the ini-
tial value is %.20g rather than %.6g, so you need to set
$# explicitly to get awk's value. (Mnemonic: # is the
number sign.)
$% The current page number of the currently selected output
channel. (Mnemonic: % is page number in nroff.)
$= The current page length (printable lines) of the
currently selected output channel. Default is 60.
(Mnemonic: = has horizontal lines.)
$- The number of lines left on the page of the currently
selected output channel. (Mnemonic: lines_on_page -
lines_printed.)
$~ The name of the current report format for the currently
selected output channel. (Mnemonic: brother to $^.)
Default is name of the filehandle.
$^ The name of the current top-of-page format for the
currently selected output channel. (Mnemonic: points to
top of page.)
Default is name of the filehandle with "_TOP" appended.
$| If set to nonzero, forces a flush after every write or
print on the currently selected output channel. Default
is 0. Note that STDOUT will typically be line buffered
if output is to the terminal and block buffered other-
wise. Setting this variable is useful primarily when you
are outputting to a pipe, such as when you are running a
perl script under rsh and want to see the output as it's
happening. (Mnemonic: when you want your pipes to be
piping hot.)
$$ The process number of the perl running this script.
(Mnemonic: same as shells.)
$? The status returned by the last pipe close, backtick (``)
command or system operator. Note that this is the status
word returned by the wait() system call, so the exit
value of the subprocess is actually ($? >> 8). $? & 255
gives which signal, if any, the process died from, and
whether there was a core dump. (Mnemonic: similar to sh
and ksh.)
$& The string matched by the last successful pattern match
(not counting any matches hidden within a BLOCK or eval
enclosed by the current BLOCK). (Mnemonic: like & in some
editors.)
$` The string preceding whatever was matched by the last
successful pattern match (not counting any matches hidden
within a BLOCK or eval enclosed by the current BLOCK).
(Mnemonic: ` often precedes a quoted string.)
$' The string following whatever was matched by the last
successful pattern match (not counting any matches hidden
within a BLOCK or eval enclosed by the current BLOCK).
(Mnemonic: ' often follows a quoted string.) Example:
$_ = 'abcdefghi';
/def/;
print "$`:$&:$'\n"; # prints abc:def:ghi
$+ The last bracket matched by the last search pattern.
This is useful if you don't know which of a set of alter-
native patterns matched. For example:
/Version: (.*)|Revision: (.*)/ && ($rev = $+);
(Mnemonic: be positive and forward looking.)
$* Set to 1 to do multiline matching within a string, 0 to
tell perl that it can assume that strings contain a sin-
gle line, for the purpose of optimizing pattern matches.
Pattern matches on strings containing multiple newlines
can produce confusing results when $* is 0. Default is
0. (Mnemonic: * matches multiple things.) Note that this
variable only influences the interpretation of ^ and $.
A literal newline can be searched for even when $* == 0.
$0 Contains the name of the file containing the perl script
being executed. Assigning to $0 modifies the argument
area that the ps(1) program sees. (Mnemonic: same as sh
and ksh.)
$<digit>
Contains the subpattern from the corresponding set of
parentheses in the last pattern matched, not counting
patterns matched in nested blocks that have been exited
already. (Mnemonic: like \digit.)
$[ The index of the first element in an array, and of the
first character in a substring. Default is 0, but you
could set it to 1 to make perl behave more like awk (or
Fortran) when subscripting and when evaluating the
index() and substr() functions. (Mnemonic: [ begins sub-
scripts.)
$] The string printed out when you say "perl -v". It can be
used to determine at the beginning of a script whether
the perl interpreter executing the script is in the right
range of versions. If used in a numeric context, returns
the version + patchlevel / 1000. Example:
# see if getc is available
($version,$patchlevel) =
$] =~ /(\d+\.\d+).*\nPatch level: (\d+)/;
print STDERR "(No filename completion available.)\n"
if $version * 1000 + $patchlevel < 2016;
or, used numerically,
warn "No checksumming!\n" if $] < 3.019;
(Mnemonic: Is this version of perl in the right bracket?)
$; The subscript separator for multi-dimensional array emu-
lation. If you refer to an associative array element as
$foo{$a,$b,$c}
it really means
$foo{join($;, $a, $b, $c)}
But don't put
@foo{$a,$b,$c} # a slice--note the @
which means
($foo{$a},$foo{$b},$foo{$c})
Default is "\034", the same as SUBSEP in awk. Note that
if your keys contain binary data there might not be any
safe value for $;. (Mnemonic: comma (the syntactic sub-
script separator) is a semi-semicolon. Yeah, I know,
it's pretty lame, but $, is already taken for something
more important.)
$! If used in a numeric context, yields the current value of
errno, with all the usual caveats. (This means that you
shouldn't depend on the value of $! to be anything in
particular unless you've gotten a specific error return
indicating a system error.) If used in a string context,
yields the corresponding system error string. You can
assign to $! in order to set errno if, for instance, you
want $! to return the string for error n, or you want to
set the exit value for the die operator. (Mnemonic: What
just went bang?)
$@ The perl syntax error message from the last eval command.
If null, the last eval parsed and executed correctly
(although the operations you invoked may have failed in
the normal fashion). (Mnemonic: Where was the syntax
error "at"?)
$< The real uid of this process. (Mnemonic: it's the uid
you came FROM, if you're running setuid.)
$> The effective uid of this process. Example:
$< = $>; # set real uid to the effective uid
($<,$>) = ($>,$<); # swap real and effective uid
(Mnemonic: it's the uid you went TO, if you're running
setuid.) Note: $< and $> can only be swapped on machines
supporting setreuid().
$( The real gid of this process. If you are on a machine
that supports membership in multiple groups simultane-
ously, gives a space separated list of groups you are in.
The first number is the one returned by getgid(), and the
subsequent ones by getgroups(), one of which may be the
same as the first number. (Mnemonic: parentheses are
used to GROUP things. The real gid is the group you
LEFT, if you're running setgid.)
$) The effective gid of this process. If you are on a
machine that supports membership in multiple groups
simultaneously, gives a space separated list of groups
you are in. The first number is the one returned by
getegid(), and the subsequent ones by getgroups(), one of
which may be the same as the first number. (Mnemonic:
parentheses are used to GROUP things. The effective gid
is the group that's RIGHT for you, if you're running set-
gid.)
Note: $<, $>, $( and $) can only be set on machines that
support the corresponding set[re][ug]id() routine. $(
and $) can only be swapped on machines supporting setre-
gid().
$: The current set of characters after which a string may be
broken to fill continuation fields (starting with ^) in a
format. Default is " \n-", to break on whitespace or
hyphens. (Mnemonic: a "colon" in poetry is a part of a
line.)
$^D The current value of the debugging flags. (Mnemonic:
value of -D switch.)
$^F The maximum system file descriptor, ordinarily 2. System
file descriptors are passed to subprocesses, while higher
file descriptors are not. During an open, system file
descriptors are preserved even if the open fails. Ordinary
file descriptors are closed before the open is attempted.
$^I The current value of the inplace-edit extension. Use
undef to disable inplace editing. (Mnemonic: value of -i
switch.)
$^L What formats output to perform a formfeed. Default is \f.
$^P The internal flag that the debugger clears so that it doesn't
debug itself. You could conceivable disable debugging yourself
by clearing it.
$^T The time at which the script began running, in seconds
since the epoch. The values returned by the -M , -A and
-C filetests are based on this value.
$^W The current value of the warning switch. (Mnemonic:
related to the -w switch.)
$^X The name that Perl itself was invoked as, from argv[0].
$ARGV contains the name of the current file when reading from
<>.
@ARGV The array ARGV contains the command line arguments
intended for the script. Note that $#ARGV is the gen-
erally number of arguments minus one, since $ARGV[0] is
the first argument, NOT the command name. See $0 for the
command name.
@INC The array INC contains the list of places to look for
perl scripts to be evaluated by the "do EXPR" command or
the "require" command. It initially consists of the
arguments to any -I command line switches, followed by
the default perl library, probably "/usr/local/lib/perl",
followed by ".", to represent the current directory.
%INC The associative array INC contains entries for each
filename that has been included via "do" or "require".
The key is the filename you specified, and the value is
the location of the file actually found. The "require"
command uses this array to determine whether a given file
has already been included.
$ENV{expr}
The associative array ENV contains your current environ-
ment. Setting a value in ENV changes the environment for
child processes.
$SIG{expr}
The associative array SIG is used to set signal handlers
for various signals. Example:
sub handler { # 1st argument is signal name
local($sig) = @_;
print "Caught a SIG$sig--shutting down\n";
close(LOG);
exit(0);
}
$SIG{'INT'} = 'handler';
$SIG{'QUIT'} = 'handler';
...
$SIG{'INT'} = 'DEFAULT'; # restore default action
$SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT
The SIG array only contains values for the signals actu-
ally set within the perl script.
æKY Perl…Packages
æC
Perl provides a mechanism for alternate namespaces to protect
packages from stomping on each others variables. By default, a
perl script starts compiling into the package known as "main".
By use of the package declaration, you can switch namespaces.
The scope of the package declaration is from the declaration
itself to the end of the enclosing block (the same scope as the
local() operator). Typically it would be the first declaration
in a file to be included by the "require" operator. You can
switch into a package in more than one place; it merely influ-
ences which symbol table is used by the compiler for the rest of
that block. You can refer to variables and filehandles in other
packages by prefixing the identifier with the package name and a
single quote. If the package name is null, the "main" package as
assumed.
Only identifiers starting with letters are stored in the packages
symbol table. All other symbols are kept in package "main". In
addition, the identifiers STDIN, STDOUT, STDERR, ARGV, ARGVOUT,
ENV, INC and SIG are forced to be in package "main", even when
used for other purposes than their built-in one. Note also that,
if you have a package called "m", "s" or "y", the you can't use
the qualified form of an identifier since it will be interpreted
instead as a pattern match, a substitution or a translation.
Eval'ed strings are compiled in the package in which the eval was
compiled in. (Assignments to $SIG{}, however, assume the signal
handler specified is in the main package. Qualify the signal
handler name if you wish to have a signal handler in a package.)
For an example, examine perldb.pl in the perl library. It ini-
tially switches to the DB package so that the debugger doesn't
interfere with variables in the script you are trying to debug.
At various points, however, it temporarily switches back to the
main package to evaluate various expressions in the context of
the main package.
The symbol table for a package happens to be stored in the asso-
ciative array of that name prepended with an underscore. The
value in each entry of the associative array is what you are
referring to when you use the *name notation. In fact, the fol-
lowing have the same effect (in package main, anyway), though the
first is more efficient because it does the symbol table lookups
at compile time:
local(*foo) = *bar;
local($_main{'foo'}) = $_main{'bar'};
You can use this to print out all the variables in a package, for
instance. Here is dumpvar.pl from the perl library:
package dumpvar;
sub main'dumpvar {
($package) = @_;
local(*stab) = eval("*_$package");
while (($key,$val) = each(%stab)) {
{
local(*entry) = $val;
if (defined $entry) {
print "\$$key = '$entry'\n";
}
if (defined @entry) {
print "\@$key = (\n";
foreach $num ($[ .. $#entry) {
print " $num\t'",$entry[$num],"'\n";
}
print ")\n";
}
if ($key ne "_$package" && defined %entry) {
print "\%$key = (\n";
foreach $key (sort keys(%entry)) {
print " $key\t'",$entry{$key},"'\n";
}
print ")\n";
}
}
}
}
Note that, even though the subroutine is compiled in package
dumpvar, the name of the subroutine is qualified so that its name
is inserted into package "main".
æKY Perl…Style
æC
Each programmer will, of course, have his or her own preferences
in regards to formatting, but there are some general guidelines
that will make your programs easier to read.
1. Just because you CAN do something a particular way doesn't
mean that you SHOULD do it that way. Perl is designed to
give you several ways to do anything, so consider picking the
most readable one. For instance
open(FOO,$foo) || die "Can't open $foo: $!";
is better than
die "Can't open $foo: $!" unless open(FOO,$foo);
because the second way hides the main point of the statement
in a modifier. On the other hand
print "Starting analysis\n" if $verbose;
is better than
$verbose && print "Starting analysis\n";
since the main point isn't whether the user typed -v or not.
Similarly, just because an operator lets you assume default
arguments doesn't mean that you have to make use of the
defaults. The defaults are there for lazy systems program-
mers writing one-shot programs. If you want your program to
be readable, consider supplying the argument.
Along the same lines, just because you can omit parentheses
in many places doesn't mean that you ought to:
return print reverse sort num values array;
return print(reverse(sort num (values(%array))));
When in doubt, parenthesize. At the very least it will let
some poor schmuck bounce on the % key in vi.
Even if you aren't in doubt, consider the mental welfare of
the person who has to maintain the code after you, and who
will probably put parens in the wrong place.
2. Don't go through silly contortions to exit a loop at the top
or the bottom, when perl provides the "last" operator so you
can exit in the middle. Just outdent it a little to make it
more visible:
line:
for (;;) {
statements;
last line if $foo;
next line if /^#/;
statements;
}
3. Don't be afraid to use loop labels--they're there to enhance
readability as well as to allow multi-level loop breaks. See
last example.
4. For portability, when using features that may not be imple-
mented on every machine, test the construct in an eval to see
if it fails. If you know what version or patchlevel a par-
ticular feature was implemented, you can test $] to see if it
will be there.
5. Choose mnemonic identifiers.
6. Be consistent.
æKY Perl…Debugging
æC
If you invoke perl with a -d switch, your script will be run
under a debugging monitor. It will halt before the first execut-
able statement and ask you for a command, such as:
h Prints out a help message.
T Stack trace.
s Single step. Executes until it reaches the beginning
of another statement.
n Next. Executes over subroutine calls, until it
reaches the beginning of the next statement.
f Finish. Executes statements until it has finished
the current subroutine.
c Continue. Executes until the next breakpoint is
reached.
c line Continue to the specified line. Inserts a one-time-
only breakpoint at the specified line.
<CR> Repeat last n or s.
l min+incr List incr+1 lines starting at min. If min is omit-
ted, starts where last listing left off. If incr is
omitted, previous value of incr is used.
l min-max List lines in the indicated range.
l line List just the indicated line.
l List next window.
- List previous window.
w line List window around line.
l subname List subroutine. If it's a long subroutine it just
lists the beginning. Use "l" to list more.
/pattern/ Regular expression search forward for pattern; the
final / is optional.
?pattern? Regular expression search backward for pattern; the
final ? is optional.
L List lines that have breakpoints or actions.
S Lists the names of all subroutines.
t Toggle trace mode on or off.
b line condition
Set a breakpoint. If line is omitted, sets a break-
point on the line that is about to be executed. If a
condition is specified, it is evaluated each time the
statement is reached and a breakpoint is taken only
if the condition is true. Breakpoints may only be
set on lines that begin an executable statement.
b subname condition
Set breakpoint at first executable line of subrou-
tine.
d line Delete breakpoint. If line is omitted, deletes the
breakpoint on the line that is about to be executed.
D Delete all breakpoints.
a line command
Set an action for line. A multi-line command may be
entered by backslashing the newlines.
A Delete all line actions.
< command Set an action to happen before every debugger prompt.
A multi-line command may be entered by backslashing
the newlines.
> command Set an action to happen after the prompt when you've
just given a command to return to executing the
script. A multi-line command may be entered by
backslashing the newlines.
V package List all variables in package. Default is main pack-
age.
! number Redo a debugging command. If number is omitted,
redoes the previous command.
! -number Redo the command that was that many commands ago.
H -number Display last n commands. Only commands longer than
one character are listed. If number is omitted,
lists them all.
q or ^D Quit.
command Execute command as a perl statement. A missing semi-
colon will be supplied.
p expr Same as "print DB'OUT expr". The DB'OUT filehandle
is opened to /dev/tty, regardless of where STDOUT may
be redirected to.
If you want to modify the debugger, copy perldb.pl from the perl
library to your current directory and modify it as necessary.
(You'll also have to put -I. on your command line.) You can do
some customization by setting up a .perldb file which contains
initialization code. For instance, you could make aliases like
these:
$DB'alias{'len'} = 's/^len(.*)/p length($1)/';
$DB'alias{'stop'} = 's/^stop (at|in)/b/';
$DB'alias{'.'} =
's/^\./p "\$DB\'sub(\$DB\'line):\t",\$DB\'line[\$DB\'line]/';
æPerSetuid
æC
Setuid Scripts
Perl is designed to make it easy to write secure setuid and set-
gid scripts. Unlike shells, which are based on multiple substi-
tution passes on each line of the script, perl uses a more con-
ventional evaluation scheme with fewer hidden "gotchas". Addi-
tionally, since the language has more built-in functionality, it
has to rely less upon external (and possibly untrustworthy) pro-
grams to accomplish its purposes.
In an unpatched 4.2 or 4.3bsd kernel, setuid scripts are intrin-
sically insecure, but this kernel feature can be disabled. If it
is, perl can emulate the setuid and setgid mechanism when it
notices the otherwise useless setuid/gid bits on perl scripts.
If the kernel feature isn't disabled, perl will complain loudly
that your setuid script is insecure. You'll need to either dis-
able the kernel setuid script feature, or put a C wrapper around
the script.
When perl is executing a setuid script, it takes special precau-
tions to prevent you from falling into any obvious traps. (In
some ways, a perl script is more secure than the corresponding C
program.) Any command line argument, environment variable, or
input is marked as "tainted", and may not be used, directly or
indirectly, in any command that invokes a subshell, or in any
command that modifies files, directories or processes. Any vari-
able that is set within an expression that has previously refer-
enced a tainted value also becomes tainted (even if it is logi-
cally impossible for the tainted value to influence the vari-
able). For example:
$foo = shift; # $foo is tainted
$bar = $foo,'bar'; # $bar is also tainted
$xxx = <>; # Tainted
$path = $ENV{'PATH'}; # Tainted, but see below
$abc = 'abc'; # Not tainted
system "echo $foo"; # Insecure
system "/bin/echo", $foo; # Secure (doesn't use sh)
system "echo $bar"; # Insecure
system "echo $abc"; # Insecure until PATH set
$ENV{'PATH'} = '/bin:/usr/bin';
$ENV{'IFS'} = '' if $ENV{'IFS'} ne '';
$path = $ENV{'PATH'}; # Not tainted
system "echo $abc"; # Is secure now!
open(FOO,"$foo"); # OK
open(FOO,">$foo"); # Not OK
open(FOO,"echo $foo|"); # Not OK, but...
open(FOO,"-|") || exec 'echo', $foo; # OK
$zzz = `echo $foo`; # Insecure, zzz tainted
unlink $abc,$foo; # Insecure
umask $foo; # Insecure
exec "echo $foo"; # Insecure
exec "echo", $foo; # Secure (doesn't use sh)
exec "sh", '-c', $foo; # Considered secure, alas
The taintedness is associated with each scalar value, so some
elements of an array can be tainted, and others not.
If you try to do something insecure, you will get a fatal error
saying something like "Insecure dependency" or "Insecure PATH".
Note that you can still write an insecure system call or exec,
but only by explicitly doing something like the last example
above. You can also bypass the tainting mechanism by referencing
subpatterns--perl presumes that if you reference a substring
using $1, $2, etc, you knew what you were doing when you wrote
the pattern:
$ARGV[0] =~ /^-P(\w+)$/;
$printer = $1; # Not tainted
This is fairly secure since \w+ doesn't match shell metacharac-
ters. Use of .+ would have been insecure, but perl doesn't check
for that, so you must be careful with your patterns. This is the
ONLY mechanism for untainting user supplied filenames if you want
to do file operations on them (unless you make $> equal to $<).
It's also possible to get into trouble with other operations that
don't care whether they use tainted values. Make judicious use
of the file tests in dealing with any user-supplied filenames.
When possible, do opens and such after setting $> = $<. Perl
doesn't prevent you from opening tainted filenames for reading,
so be careful what you print out. The tainting mechanism is
intended to prevent stupid mistakes, not to remove the need for
thought.
æKY Perl…Environment
æC
HOME Used if chdir has no argument.
LOGDIR Used if chdir has no argument and HOME is not set.
Commands Used in executing subprocesses, and in finding the script
if -S is used.
PERLLIB A comma-separated list of directories in which to look for
Perl library files before looking in the standard library
and the current directory.
PERLDB The command used to get the debugger code. If unset, uses
require 'perldb.pl'
Apart from these, perl uses no other environment variables, except
to make them available to the script being executed, and to child
processes. However, scripts running setuid would do well to exe-
cute the following lines before doing anything else, just to keep
people honest:
$ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
$ENV{'SHELL'} = '/bin/sh' if $ENV{'SHELL'} ne '';
$ENV{'IFS'} = '' if $ENV{'IFS'} ne '';
æKY Perl…Diagnostics
æC
Compilation errors will tell you the line number of the error,
with an indication of the next token or token type that was to be
examined. (In the case of a script passed to perl via -e
switches, each -e is counted as one line.)
Setuid scripts have additional constraints that can produce error
messages such as "Insecure dependency". See the section on
setuid scripts.
æKY Perl…Traps
æC
Accustomed awk users should take special note of the following:
* Semicolons are required after all simple statements in perl.
(except at the end of a block). Newline is not a statement
delimiter.
* Curly brackets are required on ifs and whiles.
* Variables begin with $ or @ in perl.
* Arrays index from 0 unless you set $[. Likewise string posi-
tions in substr() and index().
* You have to decide whether your array has numeric or string
indices.
* Associative array values do not spring into existence upon
mere reference.
* You have to decide whether you want to use string or numeric
comparisons.
* Reading an input line does not split it for you. You get to
split it yourself to an array. And the split operator has
different arguments.
* The current input line is normally in $_, not $0. It gen-
erally does not have the newline stripped. ($0 is the name
of the program executed.)
* $<digit> does not refer to fields--it refers to substrings
matched by the last match pattern.
* The print statement does not add field and record separators
unless you set $, and $\.
* You must open your files before you print to them.
* The range operator is "..", not comma. (The comma operator
works as in C.)
* The match operator is "=~", not "~". ("~" is the one's com-
plement operator, as in C.)
* The exponentiation operator is "**", not "^". ("^" is the
XOR operator, as in C.)
* The concatenation operator is ".", not the null string.
(Using the null string would render "/pat/ /pat/" unparsable,
since the third slash would be interpreted as a division
operator--the tokener is in fact slightly context sensitive
for operators like /, ?, and <. And in fact, . itself can be
the beginning of a number.)
* Next, exit and continue work differently.
* The following variables work differently
Awk Perl
ARGC $#ARGV
ARGV[0] $0
FILENAME $ARGV
FNR $. - something
FS (whatever you like)
NF $#Fld, or some such
NR $.
OFMT $#
OFS $,
ORS $\
RLENGTH length($&)
RS $/
RSTART length($`)
SUBSEP $;
* When in doubt, run the awk construct through a2p and see what
it gives you.
Cerebral C programmers should take note of the following:
* Curly brackets are required on ifs and whiles.
* You should use "elsif" rather than "else if"
* Break and continue become last and next, respectively.
* There's no switch statement.
* Variables begin with $ or @ in perl.
* Printf does not implement *.
* Comments begin with #, not /*.
* You can't take the address of anything.
* ARGV must be capitalized.
* The "system" calls link, unlink, rename, etc. return nonzero
for success, not 0.
* Signal handlers deal with signal names, not numbers.
Seasoned sed programmers should take note of the following:
* Backreferences in substitutions use $ rather than \.
* The pattern matching metacharacters (, ), and | do not have
backslashes in front.
* The range operator is .. rather than comma.
Sharp shell programmers should take note of the following:
* The backtick operator does variable interpretation without
regard to the presence of single quotes in the command.
* The backtick operator does no translation of the return
value, unlike csh.
* Shells (especially csh) do several levels of substitution on
each command line. Perl does substitution only in certain
constructs such as double quotes, backticks, angle brackets
and search patterns.
* Shells interpret scripts a little bit at a time. Perl com-
piles the whole program before executing it.
* The arguments are available via @ARGV, not $1, $2, etc.
* The environment is not automatically made available as vari-
ables.
æKY Perl…Errata
æC
The Perl book, Programming Perl, has the following omissions and
goofs.
On page 5, the examples which read
eval "/usr/bin/perl
should read
eval "exec /usr/bin/perl
On page 195, the equivalent to the System V sum program only
works for very small files. To do larger files, use
undef $/;
$checksum = unpack("%32C*",<>) % 32767;
The descriptions of alarm and sleep refer to signal SIGALARM.
These should refer to SIGALRM.
The -0 switch to set the initial value of $/ was added to Perl
after the book went to press.
The -l switch now does automatic line ending processing.
The qx// construct is now a synonym for backticks.
$0 may now be assigned to set the argument displayed by ps (1).
The new @###.## format was omitted accidentally from the descrip-
tion on formats.
It wasn't known at press time that s///ee caused multiple evalua-
tions of the replacement expression. This is to be construed as
a feature.
(LIST) x $count now does array replication.
There is now no limit on the number of parentheses in a regular
expression.
In double-quote context, more escapes are supported: \e, \a,
\x1b, \c[, \l, \L, \u, \U, \E. The latter five control up/lower
case translation.
The $/ variable may now be set to a multi-character delimiter.
There is now a g modifier on ordinary pattern matching that causes it
to iterate through a string finding multiple matches.
All of the $^X variables are new except for $^T.
The default top-of-form format for FILEHANDLE is now FILEHANDLE_TOP rather
than top.
The eval {} and sort {} constructs were added in version 4.018.
The v and V (little-endian) template options for pack and unpack were
added in 4.019.
æKY Perl…Bugs
æC
Perl is at the mercy of your machine's definitions of various
operations such as type casting, atof() and sprintf().
If your stdio requires an seek or eof between reads and writes on
a particular stream, so does perl.
(This doesn't apply to sysread() and syswrite().)
While none of the built-in data types have any arbitrary size
limits (apart from memory size), there are still a few arbitrary
limits: a given identifier may not be longer than 255 characters;
and no component of your PATH may be longer than 255 if you use -S.
A regular expression may not compile to more than 32767 bytes
internally.
Perl actually stands for Pathologically Eclectic Rubbish Lister,
but don't tell anyone I said that.
æKY Perl…Macintosh…Extensions
æC
All Macintosh specific routines are currently defined in the MacPerl
package.
æKL MacPerl'Answer
MacPerl'Ask
MacPerl'Choose
MacPerl'DebugExternals
MacPerl'DoAppleScript
MacPerl'FAccess
MacPerl'GetFileInfo
MacPerl'LoadExternals
MacPerl'Pick
MacPerl'Quit
MacPerl'Reply
MacPerl'SetFileInfo
æKY Answer
MacPerl'Answer
æDT &MacPerl'Answer(PROMPT,BUTTON1,BUTTON2,BUTTON3)
æC &MacPerl'Answer(PROMPT)
&MacPerl'Answer(PROMPT,BUTTON1)
&MacPerl'Answer(PROMPT,BUTTON1,BUTTON2)
&MacPerl'Answer(PROMPT,BUTTON1,BUTTON2,BUTTON3)
Presents to the user a dialog with 1, 2, or 3 buttons.
Examples:
&MacPerl'Answer("Nunc et in hora mortis nostrae", "Amen");
always returns 0.
&MacPerl'Answer("I refuse");
is equivalent to answer("I refuse", "OK");
&MacPerl'Answer("Delete hard disk ?", "OK", "Cancel");
returns 1 for OK, 0 for Cancel
&MacPerl'Answer("Overwrite existig file", "Overwrite", "Skip", "Cancel");
returns 2 for Overwrite, 1 for Skip, 0 for Cancel
æKY Ask
MacPerl'Ask
æDT &MacPerl'Ask(PROMPT, DEFAULT)
æC &MacPerl'Ask(PROMPT, DEFAULT)
&MacPerl'Ask(PROMPT)
Asks the user for a string. A default value may be given. Returns
undef if the dialog is cancelled.
Example:
$phone = &MacPerl'Ask("Enter your phone number:");
$name = &MacPerl'Ask("Enter your first name", "Bruce");
Useful for Australian database applications
æKY Pick
MacPerl'Pick
æDT MacPerl'Pick(PROMPT, VALUES)
æC MacPerl'Pick(PROMPT, VALUES)
Asks the user to pick a choice from a list. VALUES is a list of choices.
Returns undef if the dialog is cancelled.
Examples:
$color = MacPerl'Pick("What's your favorite color baby ?", "Red", "Green", "Gold")
æKY Choose
MacPerl'Choose
æDT &MacPerl'Choose(DOMAIN,TYPE,PROMPT,CONSTRAINT,FLAGS,DEFAULT)
æC &MacPerl'Choose(DOMAIN,TYPE,PROMPT,CONSTRAINT,FLAGS,DEFAULT)
&MacPerl'Choose(DOMAIN,TYPE,PROMPT,CONSTRAINT,FLAGS)
&MacPerl'Choose(DOMAIN,TYPE,PROMPT,CONSTRAINT)
&MacPerl'Choose(DOMAIN,TYPE,PROMPT)
Puts up a modal dialog prompting the user to choose an address.
DOMAIN specifies the communication domain, like for socket().
TYPE may be used by future communication domains to further
differentiate within a domain, but is ignored by current domains.
PROMPT is a message that will appear in the dialog. CONSTRAINT may
be set to a suitable packed value to restrict the types of acceptable
addresses.
Examples:
require "GUSI.ph";
$file =
&MacPerl'Choose(
&GUSI'AF_FILE, 0, "",
&GUSI'pack_sa_constr_file("OBJ ", "TEXT"));
Return the full pathname of an existing text
or MPW object file.
$dir = &MacPerl'Choose(&GUSI'AF_FILE, 0, "", "", &GUSI'CHOOSE_DIR);
Return the full pathname of an existing directory.
$file =
&MacPerl'Choose(
&GUSI'AF_FILE, 0, "", "",
&GUSI'CHOOSE_NEW + &GUSI'CHOOSE_DEFAULT, "yo");
Return the pathname of a new file to be created.
æKY SetFileInfo
MacPerl'SetFileInfo
æDT &MacPerl'SetFileInfo(CREATOR,TYPE,FILE...)
æC &MacPerl'SetFileInfo(CREATOR,TYPE,FILE...)
Changes the file types and creators of the file(s).
Examples:
&MacPerl'SetFileInfo("MPS ", "TEXT", yin, yang);
Turn yin and yang into MPW text files
æKY GetFileInfo
MacPerl'GetFileInfo
æDT &MacPerl'SetFileInfo(FILE)
æC &MacPerl'SetFileInfo(FILE)
In scalar context, returns the file type. In array context, returns
(creator,type).
Examples:
&MacPerl'SetFileInfo(yin);
Returns "TEXT" or ("MPS ", "TEXT").
æKY DoAppleScript
MacPerl'DoAppleScript
æDT &MacPerl'DoAppleScript(SCRIPT)
æC &MacPerl'DoAppleScript(SCRIPT)
Execute an AppleScript script.
Example:
&MacPerl'DoAppleScript(<<END_SCRIPT);
tell application "MacPerl"
make new Window
copy "Inserting text the hard way." to character 1 of front Window
end tell
END_SCRIPT
æKY Reply
MacPerl'Reply
æDT &MacPerl'Reply(ANSWER)
æC &MacPerl'Reply(ANSWER)
Reply to current DoScript request. Useful if you are calling Perl
scripts from other applications.
æKY Quit
MacPerl'Quit
æDT &MacPerl'Quit(LEVEL)
æC &MacPerl'Quit(LEVEL)
If Level is 0, don't quit after ending the script. If 1, quit if
running under a runtime version, if 2, always quit.
æKY LoadExternals
MacPerl'LoadExternals
æDT &MacPerl'LoadExternals(LIBFILE)
æC &MacPerl'LoadExternals(LIBFILE)
Load XCMD and XFCN extensions contained in file LIBFILE, which is searched
along the same path as it would be for a require. The extensions are made
accessible in the current package, unless they conatin an explicit package
name.
æKY DebugExternals
MacPerl'DebugExternals
æDT &MacPerl'DebugExternals(DEBUGLEVEL)
æC &MacPerl'DebugExternals(DEBUGLEVEL)
If DEBUGLEVEL is 0, don't print any debug information for XCMDs and XFCNs.
If 1, print information for unimplemented callbacks. If 2, print
informations for all callbacks.
æKY FAccess
MacPerl'FAccess
æDT &MacPerl'FAccess(FILE, CMD, ARG...)
æC &MacPerl'FAccess(FILE, CMD, ARG...)
When called from the tool, manipulate various information of files. To
get the command constants, it's convenient to require "FAccess.ph".
$TAB = &MacPerl'FAccess(FILE, &F_GTABINFO)
&MacPerl'FAccess(FILE, &F_STABINFO, TAB)
Manipulate tabulator setting (in spaces per tab).
($FONTNAME, $FONTSIZE) = &MacPerl'FAccess(FILE, &F_GFONTINFO)
$FONTNUM = &MacPerl'FAccess(FILE, &F_GFONTINFO)
&MacPerl'FAccess(FILE, &F_SFONTINFO, FONT [, SIZE])
Manipulate font and size information. Both font names and font numbers
are accepted for F_SFONTINFO; F_GFONTINFO returns a font name in an
array context, a font number in a scalar context.
($STARTSEL, $ENDSEL, $DISPLAYTOP) = &MacPerl'FAccess(FILE, &F_GSELINFO)
$STARTSEL = &MacPerl'FAccess(FILE, &F_GSELINFO)
&MacPerl'FAccess(FILE, &F_SSELINFO, $STARTSEL, $ENDSEL [, $DISPLAYTOP])
Manipulate the MPW selection of a file.
($LEFT, $TOP, $RIGHT, $BOTTOM) = &MacPerl'FAccess(FILE, &F_GWININFO)
$TOP = &MacPerl'FAccess(FILE, &F_GWININFO)
&MacPerl'FAccess(FILE, &F_SWININFO, LEFT, TOP [, RIGHT, BOTTOM])
Manipulate the window position.