RC

Section: User Commands (1)
Updated: 28 April 1991
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NAME

rc - shell

SYNOPSIS

rc [-eixvldnpo] [-c command] [arguments]

DESCRIPTION

rc is a command interpreter and programming language similar to sh(1). It is based on the AT&T Plan 9 shell of the same name. The shell offers a C-like syntax (much more so than the C shell), and a powerful mechanism for manipulating variables. It is reasonably small and reasonably fast, especially when compared to contemporary shells. Its use is intended to be interactive, but the language lends itself well to scripts.

OPTIONS

R-e: If the R-e option is present, then rc will exit if the exit status of a command is false (nonzero). rc will not exit, however, if a conditional fails, e.g., an Rif() command.
R-i: If the R-i option is present or if the input to rc is from a terminal (as determined by isatty(3)) then rc will be in interactive mode. That is, a prompt (from R$prompt(1)R) R$prompt(1) will be printed before an input line is taken, and rc will ignore the signals RSIGINT and RSIGQUITR. RSIGQUIT
R-x: This option will make rc print every command on standard error before it is executed. It can be useful for debugging rc scripts.
R-v: This option will echo input to rc on standard error as it is read.
R-l: If the R-l option is present, or if rc's Rargv[0][0] is a dash R(R-R), R(R- R( then rc will behave as a login shell. That is, it will try to run commands present in R$home/.rcrcR, R$home/.rcrc if this file exists, before reading any other input.
R-d: This flag causes rc not to ignore RSIGQUIT or RSIGTERMR. RSIGTERM Thus rc can be made to dump core if sent RSIGQUITR. RSIGQUIT This option is only useful for debugging rc.
R-n: This flag causes rc to read its input and parse it, but not to execute any commands. This is useful for syntax checking on scripts. If used in combination with the R-x option, rc will print each command as it is parsed in a form similar to the one used for exporting functions into the environment.
R-p: This flag prevents rc from initializing shell functions from the environment. This allows rc to run in a protected mode, whereby it becomes more difficult for an rc script to be subverted by placing false commands in the environment. (Note that this presence of this option does NOT mean that it is safe to run setuid rc scripts; the usual caveats about the setuid bit still apply.)
R-o: This flag prevents the usual practice of trying to open R/dev/null on file descriptors 0, 1, and 2, if any of those descriptors are inherited closed.
R-c: If R-c is present, commands are executed from the immediately following argument. Any further arguments to rc are placed in R$*R. R$*

COMMANDS

A simple command is a sequence of words, separated by white space (space and tab) characters that ends with a newline, semicolon R(R;R), R(R; R( or ampersand R(R&R). R(R& R( The first word of a command is the name of that command. If the name begins with R/R, R/ R./R, R./ or R../R, R../ then the name is used as an absolute path name referring to an executable file. Otherwise, the name of the command is looked up in a table of shell functions, builtin commands, or as a file in the directories named by R$pathR. R$path

Background Tasks

A command ending with a R& is run in the background; that is, the shell returns immediately rather than waiting for the command to complete. Background commands have R/dev/null connected to their standard input unless an explicit redirection for standard input is used.

Subshells

A command prefixed with an at-sign R(R@R) R(R@ R( is executed in a subshell. This insulates the parent shell from the effects of state changing operations such as a cd or a variable assignment. For example:





R@ {cd ..; make}

will run make(1) in the parent directory R(R..R), R(R.. R( but leaves the shell running in the current directory.

Line continuation

A long logical line may be continued over several physical lines by terminating each line (except the last) with a backslash R(R\R). R(R\ R( The backslash-newline sequence is treated as a space. A backslash is not otherwise special to rc. (In addition, inside quotes a backslash loses its special meaning even when it is followed by a newline.)

Quoting

rc interprets several characters specially; special characters automatically terminate words. The following characters are special:





R# ; & | ^ $ = ` ' { } ( ) < >

The single quote R(R'R) R(R' R( prevents special treatment of any character other than itself. All characters, including control characters, newlines, and backslashes between two quote characters are treated as an uninterpreted string. A quote character itself may be quoted by placing two quotes in a row. The minimal sequence needed to enter the quote character is R''''R. R'''' The empty string is represented by R''R. R'' Thus:





Recho 'What''s the plan, Stan?'

prints out





RWhat's the plan, Stan?

The number sign R(R#R) R(R# R( begins a comment in rc. All characters up to but not including the next newline are ignored. Note that backslash continuation does not work inside a comment, i.e., the backslash is ignored along with everything else.

Grouping

Zero or more commands may be grouped within braces R(``R{R'' R(``R{ R(`` and R``R}R''), R``R} R`` and are then treated as one command. Braces do not otherwise define scope; they are used only for command grouping. In particular, be wary of the command:





Rfor (i) {





R    command





R} | command

Since pipe binds tighter than RforR, Rfor this command does not perform what the user expects it to. Instead, enclose the whole Rfor statement in braces:





R{for (i) command} | command

Fortunately, rc's grammar is simple enough that a (confident) user can understand it by examining the skeletal yacc(1) grammar at the end of this man page (see the section entitled GRAMMAR).

Input and output

The standard output may be redirected to a file with





Rcommand > file

and the standard input may be taken from a file with





Rcommand < file

File descriptors other than 0 and 1 may be specified also. For example, to redirect standard error to a file, use:





Rcommand >[2] file

In order to duplicate a file descriptor, use R>[InR=ImR]. R>[InR=Im R>[InR= R>[In R>[ Thus to redirect both standard output and standard error to the same file, use





Rcommand > file >[2=1]

To close a file descriptor that may be open, use R>[InR=]. R>[In R>[ For example, to close file descriptor 7:





Rcommand >[7=]

In order to place the output of a command at the end of an already existing file, use:





Rcommand >> file

If the file does not exist, then it is created.

``Here documents'' are supported as in sh with the use of





Rcommand << 'eof-marker'

If the end-of-file marker is enclosed in quotes, then no variable substitution occurs inside the here document. Otherwise, every variable is substituted by its space-separated-list value (see Flat Lists, below), and if a R^ character follows a variable name, it is deleted. This allows the unambiguous use of variables adjacent to text, as in





R$variable^follow

To include a literal R$ in a here document when an unquoted end-of-file marker is being used, enter it as R$$R. R$$

Additionally, rc supports ``here strings'', which are like here documents, except that input is taken directly from a string on the command line. Its use is illustrated here:





Rcat <<< 'this is a here string' | wc

(This feature enables rc to export functions using here documents into the environment; the author does not expect users to find this feature useful.)

Pipes





Rcommand |[2] wc

The exit status of a pipeline is considered true if and only if every command in the pipeline exits true.

Commands as Arguments

Some commands, like cmp(1) or diff(1), take their arguments on the command line, and do not read input from standard input. It is convenient sometimes to build nonlinear pipelines so that a command like cmp can read the output of two other commands at once. rc does it like this:





Rcmp <{command} <{command}

compares the output of the two commands in braces. A note: since this form of redirection is implemented with some kind of pipe, and since one cannot lseek(2) on a pipe, commands that use lseek(2) will hang. For example, most versions of diff(1) use lseek(2) on their inputs.

Data can be sent down a pipe to several commands using tee(1) and the output version of this notation:





Recho hi there | tee >{sed 's/^/p1 /'} >{sed 's/^/p2 /'}

CONTROL STRUCTURES

The following may be used for control flow in rc:

If-else Statements

Rif (ItestR) { Rif (Itest Rif (
cmd

R} else Icmd R} else

The test is executed, and if its return status is zero, the first command is executed, otherwise the second is. Braces are not mandatory around the commands. However, an Relse statement is valid only if it follows a close-brace on the same line. Otherwise, the Rif is taken to be a simple-if:





Rif (test)





R    command

While and For Loops

Rwhile (ItestR)I cmd Rwhile (ItestR) Rwhile (Itest Rwhile (

rc executes the test and performs the command as long as the test is true.

Rfor (IvarR inI listR)I cmd Rfor (IvarR inI listR) Rfor (IvarR inI list Rfor (IvarR in Rfor (Ivar Rfor (

rc sets var to each element of list (which may contain variables and backquote substitutions) and runs cmd. If R``Rin R`` list'' is omitted, then rc will set var to each element of R$* (excluding R$0R). R$0 For example:





Rfor (i in `{ls -F | grep '\*$' | sed 's/\*$//'}) { commands }

will set R$i to the name of each file in the current directory that is executable.

Switch

Rswitch (IlistR) { caseI ...R } Rswitch (IlistR) { caseI ... Rswitch (IlistR) { case Rswitch (Ilist Rswitch (: rc looks inside the braces after a Rswitch for statements beginning with the word RcaseR. Rcase If any of the patterns following Rcase match the list supplied to RswitchR, Rswitch then the commands up until the next Rcase statement are executed. The metacharacters R*R, R* R[ or R? should not be quoted; matching is performed only against the strings in list, not against file names. (Matching for case statements is the same as for the R~ command.)

Logical Operators

There are a number of operators in rc which depend on the exit status of a command.





Rcommand && command

executes the first command and then executes the second command if and only if the first command exits with a zero exit status (``true'' in Unix).





Rcommand || command

executes the first command executing the second command if and only if the second command exits with a nonzero exit status (``false'' in Unix).





R! command

negates the exit status of a command.

PATTERN MATCHING

There are two forms of pattern matching in rc. One is traditional shell globbing. This occurs in matching for file names in argument lists:





Rcommand argument argument ...

When the characters R*R, R* R[ or R? occur in an argument or command, rc looks at the argument as a pattern for matching against files. (Contrary to the behavior other shells exhibit, rc will only perform pattern matching if a metacharacter occurs unquoted and literally in the input. Thus,





Rfoo='*'





Recho $foo

will always echo just a star. In order for non-literal metacharacters to be expanded, an Reval statement must be used in order to rescan the input.) Pattern matching occurs according to the following rules: a R* matches any number (including zero) of characters. A R? matches any single character, and a R[ followed by a number of characters followed by a R] matches a single character in that class. The rules for character class matching are the same as those for ed(1), with the exception that character class negation is achieved with the tilde R(R~R), R(R~ R( not the caret R(R^R), R(R^ R( since the caret already means something else in rc.

rc also matches patterns against strings with the R~ command:





R~ subject pattern pattern ...

R~ sets R$status to zero if and only if a supplied pattern matches any single element of the subject list. Thus





R~ foo f*

sets status to zero, while





R~ (bar baz) f*

sets status to one. The null list is matched by the null list, so





R~ $foo ()

checks to see whether R$foo is empty or not. This may also be achieved by the test





R~ $#foo 0

Note that inside a R~ command rc does not match patterns against file names, so it is not necessary to quote the characters R*R, R* R[ and R?R. R? However, rc does expand the glob the subject against filenames if it contains metacharacters. Thus, the command





R~ * ?

returns true if any of the files in the current directory have a single-character name. (Note that if the R~ command is given a list as its first argument, then a successful match against any of the elements of that list will cause R~ to return true. For example:





R~ (foo goo zoo) z*

is true.)

LISTS AND VARIABLES

The primary data structure in rc is the list, which is a sequence of words. Parentheses are used to group lists. The empty list is represented by R()R. R() Lists have no hierarchical structure; a list inside another list is expanded so the outer list contains all the elements of the inner list. Thus, the following are all equivalent





Rone two three






R(one two three)






R((one) () ((two three)))

Note that the null string, R''R, R'' and the null list, R()R, R() are two very different things. Assigning the null string to variable is a valid operation, but it does not remove its definition. For example, if R$a is set to R''R, R'' then R$#aR, R$#a returns a 1.

List Concatenation

Two lists may be joined by the concatenation operator R(R^R). R(R^ R( A single word is treated as a list of length one, so





Recho foo^bar

produces the output





Rfoobar

For lists of more than one element, concatenation works according to the following rules: if the two lists have the same number of elements, then concatenation is pairwise:





Recho (a- b- c-)^(1 2 3)

produces the output





Ra-1 b-2 c-3

Otherwise, one of the lists must have a single element, and then the concatenation is distributive:





Rcc -^(O g c) (malloc alloca)^.c

has the effect of performing the command





Rcc -O -g -c malloc.c alloca.c

Free Carets

rc inserts carets (concatenation operators) for free in certain situations, in order to save some typing on the user's behalf. For example, the above example could also be typed in as:





Ropts=(O g c) files=(malloc alloca) cc -$opts $files.c

rc takes care to insert a free-caret between the R``R-R'' R``R- R`` and R$optsR, R$opts as well as between R$files and R.cR. R.c The rule for free carets is as follows: if a word or keyword is immediately followed by another word, keyword, dollar-sign or backquote, then rc inserts a caret between them.

Variables

A list may be assigned to a variable, using the notation:

var  =  list

Any sequence of non-special characters, except a sequence including only digits, may be used as a variable name. All user-defined variables are exported into the environment.

The value of a variable is referenced with the notation:







R$IvarR$

Any variable which has not been assigned a value returns the null list, R()R, R() when referenced. In addition, multiple references are allowed:





Ra=foo





Rb=a





Recho $$b

prints





Rfoo

A variable's definition may also be removed by assigning the null list to a variable:

var =()

For ``free careting'' to work correctly, rc must make certain assumptions about what characters may appear in a variable name. rc assumes that a variable name consists only of alphanumeric characters, underscore R(R_R) R(R_ R( and star R(R*R). R(R* R( To reference a variable with other characters in its name, quote the variable name. Thus:





Recho $'we$IrdVariab!le'

Local Variables

Any number of variable assignments may be made local to a single command by typing:





Ra=foo b=bar ... command

The command may be a compound command, so for example:





Rpath=. ifs=() {







R    R...R    






R}

sets Rpath to R. and removes Rifs for the duration of one long compound command.

Variable Subscripts

Variables may be subscripted with the notation









R$var(InR)R$var(In
R$var(

where n is a list of integers (origin 1). The list of subscripts need not be in order or even unique. Thus, if





Ra=(one two three)

then





Recho $a(3 3 3)

prints





Rthree three three

If n references a nonexistent element, then R$var(InR) R$var(In R$var( returns the null list. The notation R$In, R$ where n is an integer, is a shorthand for R$*(InR). R$*(In R$*( Thus, rc's arguments may be referred to as R$1R, R$1 R$2R, R$2 and so on.

Note also that the list of subscripts may be given by any of rc's list operations:





R$var(`{awk 'BEGIN{for(i=1;i<=10;i++)print i;exit; }'})

returns the first 10 elements of R$varR. R$var

To count the number of elements in a variable, use





R$#var

This returns a single-element list, with the number of elements in R$varR. R$var

Flat Lists

In order to create a single-element list from a multi-element list, with the components space-separated, use





R$^var

This is useful when the normal list concatenation rules need to be bypassed. For example, to append a single period at the end of R$pathR, R$path use:





Recho $^path.

Backquote Substitution

A list may be formed from the output of a command by using backquote substitution:





R`{ command }

returns a list formed from the standard output of the command in braces. R$ifs is used to split the output into list elements. By default, R$ifs has the value space-tab-newline. The braces may be omitted if the command is a single word. Thus R`ls may be used instead of R`{ls}R. R`{ls} This last feature is useful when defining functions that expand to useful argument lists. A frequent use is:





Rfn src { echo *.[chy] }

followed by





Rwc `src

(This will print out a word-count of all C source files in the current directory.)

In order to override the value of R$ifs for a single backquote substitution, use:





R`` (ifs-list) { command }

R$ifs will be temporarily ignored and the command's output will be split as specified by the list following the double backquote. For example:





R`` ($nl :) {cat /etc/passwd}

splits up R/etc/passwd into fields, assuming that R$nl contains a newline as its value.

SPECIAL VARIABLES

Several variables are known to rc and are treated specially.

R*

The argument list of rc. R$1, $2, etc. are the same as R$*(1)R, R$*(1) R$*(2)R, R$*(2) etc. The variable R$0 holds the value of Rargv[0] with which rc was invoked. Additionally, R$0 is set to the name of a function for the duration of the execution of that function, and R$0 is also set to the name of the file being interpreted for the duration of a R. command.

Rapid

The process ID of the last process started in the background.

Rapids

The process IDs of any background processes which are outstanding or which have died and have not been waited for yet.

Rcdpath

A list of directories to search for the target of a cd command. The empty string stands for the current directory. Note that if the R$cdpath variable does not contain the current directory, then the current directory will not be searched; this allows directory searching to begin in a directory other than the current directory. Note also that an assignment to R$cdpath causes an automatic assignment to R$CDPATHR, R$CDPATH and vice-versa.

Rhistory

R$history contains the name of a file to which commands are appended as rc reads them. This facilitates the use of a stand-alone history program (such as history(1)) which parses the contents of the history file and presents them to rc for reinterpretation. If R$history is not set, then rc does not append commands to any file.

Rhome

The default directory for the builtin cd command and is the directory in which rc looks to find its initialization file, R.rcrcR, R.rcrc if rc has been started up as a login shell. Like R$cdpath and R$CDPATHR, R$CDPATH R$home and R$HOME are aliased to each other.

Rifs

The internal field separator, used for splitting up the output of backquote commands for digestion as a list.

Rpath

This is a list of directories to search in for commands. The empty string stands for the current directory. Note that like R$cdpath and R$CDPATHR, R$CDPATH R$path and R$PATH are aliased to each other. If R$path or R$PATH is not set at startup time, R$path assumes a default value suitable for your system. This is typically R(/usr/ucb /usr/bin /bin .)

Rpid

The process ID of the currently running rc.

Rprompt

This variable holds the two prompts (in list form, of course) that rc prints. R$prompt(1) is printed before each command is read, and R$prompt(2) is printed when input is expected to continue on the next line. rc sets R$prompt to R('; ' '') by default. The reason for this is that it enables an rc user to grab commands from previous lines using a mouse, and to present them to rc for re-interpretation; the semicolon prompt is simply ignored by rc. The null R$prompt(2) also has its justification: an rc script, when typed interactively, will not leave R$prompt(2)R's R$prompt(2) on the screen, and can therefore be grabbed by a mouse and placed directly into a file for use as a shell script, without further editing being necessary.

RpromptR (function) Rprompt

If this function is set, then it gets executed every time rc is about to print R$prompt(1)R. R$prompt(1)

Rstatus

The exit status of the last command. If the command exited with a numeric value, that number is the status. If the died with a signal, the status is the name of that signal; if a core file was created, the string R``R+coreR'' R``R+core R`` is appended. The value of R$status for a pipeline is a list, with one entry, as above, for each process in the pipeline. For example, the command





Rls | wc

usually sets R$status to R(0 0)R. R(0 0)

The values of R$pathR, R$path R$cdpathR, R$cdpath and R$home are derived from the environment values of R$PATHR, R$PATH R$CDPATHR, R$CDPATH and R$HOMER. R$HOME Otherwise, they are derived from the environment values of R$pathR, R$path R$cdpath and R$homeR. R$home This is for compatibility with other Unix programs, like sh(1). R$PATH and R$CDPATH are assumed to be colon-separated lists.

FUNCTIONS

rc functions are identical to rc scripts, except that they are stored in memory and are automatically exported into the environment. A shell function is declared as:





Rfn name { commands }

rc scans the definition until the close-brace, so the function can span more than one line. The function definition may be removed by typing





Rfn name

(One or more names may be specified. With an accompanying definition, all names receive the same definition. This is sometimes useful for assigning the same signal handler to many signals. Without a definition, all named functions are deleted.) When a function is executed, R$* is set to the arguments to that function for the duration of the command. Thus a reasonable definition for RlR, Rl a shorthand for ls(1), could be:





Rfn l { ls -FC $* }

but not





Rfn l { ls -FC }

INTERRUPTS AND SIGNALS

rc recognizes a number of signals, and allows the user to define shell functions which act as signal handlers. rc by default traps RSIGINT when it is in interactive mode. RSIGQUIT and RSIGTERM are ignored, unless rc has been invoked with the R-d flag. However, user-defined signal handlers may be written for these and all other signals. The way to define a signal handler is to write a function by the name of the signal in lower case. Thus:





Rfn sighup { echo hangup; rm /tmp/rc$pid.*; exit }

In addition to Unix signals, rc recognizes the artificial signal RSIGEXIT which occurs as rc is about to exit.

In order to remove a signal handler's definition, remove it as though it were a regular function. For example:





Rfn sigint

returns the handler of RSIGINT to the default value. In order to ignore a signal, set the signal handler's value to R{}R. R{} Thus:





Rfn sigint {}

causes SIGINT to be ignored by the shell. Only signals that are being ignored are passed on to programs run by rc; signal functions are not exported.

On System V-based Unix systems, rc will not allow you to trap RSIGCLDR. RSIGCLD

BUILTIN COMMANDS

Builtin commands execute in the context of the shell, but otherwise behave exactly like other commands. Although !, ~ and @ are not strictly speaking builtin commands, they can usually be used as such.

. [-i] file [arg ...]

Reads file as input to rc and executes its contents. With a R-i flag, input is interactive. Thus from within a shell script,





R. -i /dev/tty

does the ``right'' thing.

break

Breaks from the innermost Rfor or RwhileR, Rwhile as in C. It is an error to invoke break outside of a loop. (Note that there is no break keyword between commands in Rswitch statements, unlike C.)

builtin command [arg ...]

Executes the command ignoring any function definition of the same name. This command is present to allow functions with the same names as builtins to use the underlying builtin or binary.

cd [directory]

Changes the current directory to directory. The variable R$cdpath is searched for possible locations of directory, analogous to the searching of R$path for executable files. With no argument, cd changes the current directory to R$homeR. R$home

echo [-n] [--] [arg ...]

Prints its arguments to standard output, terminated by a newline. Arguments are separated by spaces. If the first argument is R-n no final newline is printed. If the first argument is R--R, R-- then all other arguments are echoed literally. This is used for echoing a literal R-nR. R-n

eval [list]

Concatenates the elements of list with spaces and feeds the resulting string to rc for re-scanning. This is the only time input is rescanned in rc.

exec [arg ...]

Replaces rc with the given command. If the exec contains only redirections, then these redirections apply to the current shell and the shell does not exit. For example,





Rexec >[2] err.out

places further output to standard error in the file err.out.

exit [status]

Cause the current shell to exit with the given exit status. If no argument is given, the current value of R$status is used.

limit [-h] [resource [value]]

Similar to the csh(1) limit builtin, this command operates upon the BSD-style limits of a process. The R-h flag displays/alters the hard limits. The resources which can be shown or altered are cputime, filesize, datasize, stacksize, coredumpsize and memoryuse. For example:





Rlimit coredumpsize 0

disables core dumps.

newpgrp

Puts rc into a new process group. This builtin is useful for making rc behave like a job-control shell in a hostile environment. One example is the NeXT Terminal program, which implicitly assumes that each shell it forks will put itself into a new process group.

return [n]

Returns from the current function, with status n, where n is a single value or a list of possible exit statuses. Thus it is legal to have





Rreturn (sigpipe 1 2 3)

(This is commonly used to allow a function to return with the exit status of a previously executed pipeline of commands.) If n is omitted, then R$status is left unchanged. It is an error to invoke return when not inside a function.

shift [n]

Deletes n elements from the beginning of R$* and shifts the other elements down by n. n defaults to 1. (Note that R$0 is not affected by shift.)

umask [mask]

Sets the current umask (see umask(2)) to the octal mask. If no argument is present, the current mask value is printed.

wait [pid]

Waits for the specified pid, which must have been started by rc. If no pid is specified, rc waits for any child process to exit.

whatis [-s] [--] [name ...]

Prints a definition of the named objects. For variables, their values are printed; for functions, their definitions are; and for executable files, path names are printed. Without arguments, whatis prints the values of all shell variables and functions. With a R-s argument, whatis also prints out a list of available signals and their handlers (if any). Note that whatis output is suitable for input to rc; by saving the output of whatis in a file, it should be possible to recreate the state of rc by sourcing this file with a R. command. Another note: Rwhatis -s > file cannot be used to store the state of rc's signal handlers in a file, because builtins with redirections are run in a subshell, and rc always restores signal handlers to their default value after a Rfork()R. Rfork()

Since whatis uses getopt(3) to parse its arguments, you can use the special argument R-- to terminate its options. This allows you to use names beginning with a dash, such as the history(1) commands. For example,





Rwhatis -- -p

GRAMMAR

Here is rc's grammar, edited to remove semantic actions.

R%term ANDAND BACKBACK BANG CASE COUNT DUP ELSE END FLAT FN FOR IF IN
%term OROR PIPE REDIR SUB SUBSHELL SWITCH TWIDDLE WHILE WORD HUH

%left WHILE ')' ELSE
%left ANDAND OROR '\n'
%left BANG SUBSHELL
%left PIPE
%right '$'
%left SUB

%start rc

%%

rc: line end
        | error end

end: END /* EOF */ | '\n'

cmdsa: cmd ';' | cmd '&'

line: cmd | cmdsa line

body: cmd | cmdsan body

cmdsan: cmdsa | cmd '\n'

brace: '{' body '}'

paren: '(' body ')'

assign: first '=' word

epilog: /* empty */ | redir epilog

redir: DUP | REDIR word

case: CASE words ';' | CASE words '\n'

cbody: cmd | case cbody | cmdsan cbody

iftail: cmd     %prec ELSE
        | brace ELSE optnl cmd

cmd     : /* empty */   %prec WHILE
        | simple
        | brace epilog
        | IF paren optnl iftail
        | FOR '(' word IN words ')' optnl cmd
        | FOR '(' word ')' optnl cmd
        | WHILE paren optnl cmd 
        | SWITCH '(' word ')' optnl '{' cbody '}'
        | TWIDDLE optcaret word words
        | cmd ANDAND optnl cmd
        | cmd OROR optnl cmd
        | cmd PIPE optnl cmd
        | redir cmd     %prec BANG
        | assign cmd    %prec BANG
        | BANG optcaret cmd
        | SUBSHELL optcaret cmd
        | FN words brace
        | FN words

optcaret: /* empty */ | '^'

simple: first | simple word | simple redir

first: comword | first '^' sword

sword: comword | keyword

word: sword | word '^' sword

comword: '$' sword
        | '$' sword SUB words ')'
        | COUNT sword
        | FLAT sword
        | '`' sword
        | '`' brace
        | BACKBACK word brace | BACKBACK word sword
        | '(' words ')'
        | REDIR brace
        | WORD

keyword: FOR | IN | WHILE | IF | SWITCH
        | FN | ELSE | CASE | TWIDDLE | BANG | SUBSHELL

words: /* empty */ | words word

optnl: /* empty */ | optnl '\n'

FILES

R$HOME/.rcrcR, R$HOME/.rcrc R/tmp/rc*R, R/tmp/rc* R/dev/null

CREDITS

rc was written by Byron Rakitzis, with valuable help from Paul Haahr, Hugh Redelmeier and David Sanderson. The design of this shell has been copied from the rc that Tom Duff wrote at Bell Labs.

BUGS

On systems that support R/dev/fdR, R/dev/fd R<{foo} style redirection is implemented that way. However, on other systems it is implemented with named pipes, and it is sometimes possible to foil rc into removing the FIFO it places in R/tmp prematurely, or it is even possible to cause rc to hang.

The functionality of shift should be available for variables other than R$*R. R$*

echo is built in only for performance reasons, which is a bad idea.

There should be a way to avoid exporting a variable.

The R$^var notation for flattening should allow for using an arbitrary separating character, not just space.

Bug reports should be mailed to Rbyron@archone.tamu.eduR. Rbyron@archone.tamu.edu

INCOMPATIBILITIES

Here is a list of features which distinguish this incarnation of rc from the one described in the Bell Labs manual pages:

The treatment of RifR-Relse RifR- Rif is different in the v10 rc: that version uses an Rif not clause which gets executed if the preceding Rif test does not succeed.

Backquotes are slightly different in v10 rc: a backquote must always be followed by a left-brace. This restriction is not present for single-word commands in this rc.

The following are all new with this version of rc: The R-n option, the list flattening operator, here strings (they facilitate exporting of functions with here documents into the environment), the return and break keywords, the echo builtin, the support for the GNU readline(3) library and the support for the Rprompt function. This rc also sets R$0 to the name of a function being executed/file being sourced.