Frozen Fish 1: Amiga/FrozenFish-Apr94.iso/bbs/gnu/make-3.70-bin.lha/info/make.info-6

GNU Info File | 1994-02-21 | 48KB | 870 lines

This is Info file make.info, produced by Makeinfo-1.54 from the input
file ./make.texinfo.
   This file documents the GNU Make utility, which determines
automatically which pieces of a large program need to be recompiled,
and issues the commands to recompile them.
   This is Edition 0.45, last updated 14 December 1993, of `The GNU
Make Manual', for `make', Version 3.70 Beta.
   Copyright (C) 1988, '89, '90, '91, '92, '93 Free Software
Foundation, Inc.
   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Free Software Foundation.
File: make.info,  Node: Suffix Rules,  Next: Search Algorithm,  Prev: Last Resort,  Up: Implicit Rules
Old-Fashioned Suffix Rules
==========================
   "Suffix rules" are the old-fashioned way of defining implicit rules
for `make'.  Suffix rules are obsolete because pattern rules are more
general and clearer.  They are supported in GNU `make' for
compatibility with old makefiles.  They come in two kinds:
"double-suffix" and "single-suffix".
   A double-suffix rule is defined by a pair of suffixes: the target
suffix and the source suffix.  It matches any file whose name ends with
the target suffix.  The corresponding implicit dependency is made by
replacing the target suffix with the source suffix in the file name.  A
two-suffix rule whose target and source suffixes are `.o' and `.c' is
equivalent to the pattern rule `%.o : %.c'.
   A single-suffix rule is defined by a single suffix, which is the
source suffix.  It matches any file name, and the corresponding implicit
dependency name is made by appending the source suffix.  A single-suffix
rule whose source suffix is `.c' is equivalent to the pattern rule `% :
%.c'.
   Suffix rule definitions are recognized by comparing each rule's
target against a defined list of known suffixes.  When `make' sees a
rule whose target is a known suffix, this rule is considered a
single-suffix rule.  When `make' sees a rule whose target is two known
suffixes concatenated, this rule is taken as a double-suffix rule.
   For example, `.c' and `.o' are both on the default list of known
suffixes.  Therefore, if you define a rule whose target is `.c.o',
`make' takes it to be a double-suffix rule with source suffix `.c' and
target suffix `.o'.  Here is the old-fashioned way to define the rule
for compiling a C source file:
     .c.o:
             $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $<
   Suffix rules cannot have any dependencies of their own.  If they
have any, they are treated as normal files with funny names, not as
suffix rules.  Thus, the rule:
     .c.o: foo.h
             $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $<
tells how to make the file `.c.o' from the dependency file `foo.h', and
is not at all like the pattern rule:
     %.o: %.c foo.h
             $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $<
which tells how to make `.o' files from `.c' files, and makes all `.o'
files using this pattern rule also depend on `foo.h'.
   Suffix rules with no commands are also meaningless.  They do not
remove previous rules as do pattern rules with no commands (*note
Canceling Implicit Rules: Canceling Rules.).  They simply enter the
suffix or pair of suffixes concatenated as a target in the data base.
   The known suffixes are simply the names of the dependencies of the
special target `.SUFFIXES'.  You can add your own suffixes by writing a
rule for `.SUFFIXES' that adds more dependencies, as in:
     .SUFFIXES: .hack .win
which adds `.hack' and `.win' to the end of the list of suffixes.
   If you wish to eliminate the default known suffixes instead of just
adding to them, write a rule for `.SUFFIXES' with no dependencies.  By
special dispensation, this eliminates all existing dependencies of
`.SUFFIXES'.  You can then write another rule to add the suffixes you
want.  For example,
     .SUFFIXES:            # Delete the default suffixes
     .SUFFIXES: .c .o .h   # Define our suffix list
   The `-r' or `--no-builtin-rules' flag causes the default list of
suffixes to be empty.
   The variable `SUFFIXES' is defined to the default list of suffixes
before `make' reads any makefiles.  You can change the list of suffixes
with a rule for the special target `.SUFFIXES', but that does not alter
this variable.
File: make.info,  Node: Search Algorithm,  Prev: Suffix Rules,  Up: Implicit Rules
Implicit Rule Search Algorithm
==============================
   Here is the procedure `make' uses for searching for an implicit rule
for a target T.  This procedure is followed for each double-colon rule
with no commands, for each target of ordinary rules none of which have
commands, and for each dependency that is not the target of any rule.
It is also followed recursively for dependencies that come from implicit
rules, in the search for a chain of rules.
   Suffix rules are not mentioned in this algorithm because suffix
rules are converted to equivalent pattern rules once the makefiles have
been read in.
   For an archive member target of the form `ARCHIVE(MEMBER)', the
following algorithm is run twice, first using the entire target name T,
and second using `(MEMBER)' as the target T if the first run found no
rule.
  1. Split T into a directory part, called D, and the rest, called N.
     For example, if T is `src/foo.o', then D is `src/' and N is
     `foo.o'.
  2. Make a list of all the pattern rules one of whose targets matches
     T or N.  If the target pattern contains a slash, it is matched
     against T; otherwise, against N.
  3. If any rule in that list is *not* a match-anything rule, then
     remove all nonterminal match-anything rules from the list.
  4. Remove from the list all rules with no commands.
  5. For each pattern rule in the list:
       a. Find the stem S, which is the nonempty part of T or N matched
          by the `%' in the target pattern.
       b. Compute the dependency names by substituting S for `%'; if
          the target pattern does not contain a slash, append D to the
          front of each dependency name.
       c. Test whether all the dependencies exist or ought to exist.
          (If a file name is mentioned in the makefile as a target or
          as an explicit dependency, then we say it ought to exist.)
          If all dependencies exist or ought to exist, or there are no
          dependencies, then this rule applies.
  6. If no pattern rule has been found so far, try harder.  For each
     pattern rule in the list:
       a. If the rule is terminal, ignore it and go on to the next rule.
       b. Compute the dependency names as before.
       c. Test whether all the dependencies exist or ought to exist.
       d. For each dependency that does not exist, follow this algorithm
          recursively to see if the dependency can be made by an
          implicit rule.
       e. If all dependencies exist, ought to exist, or can be made by
          implicit rules, then this rule applies.
  7. If no implicit rule applies, the rule for `.DEFAULT', if any,
     applies.  In that case, give T the same commands that `.DEFAULT'
     has.  Otherwise, there are no commands for T.
   Once a rule that applies has been found, for each target pattern of
the rule other than the one that matched T or N, the `%' in the pattern
is replaced with S and the resultant file name is stored until the
commands to remake the target file T are executed.  After these
commands are executed, each of these stored file names are entered into
the data base and marked as having been updated and having the same
update status as the file T.
   When the commands of a pattern rule are executed for T, the automatic
variables are set corresponding to the target and dependencies.  *Note
Automatic Variables: Automatic.
File: make.info,  Node: Archives,  Next: Features,  Prev: Implicit Rules,  Up: Top
Using `make' to Update Archive Files
************************************
   "Archive files" are files containing named subfiles called
"members"; they are maintained with the program `ar' and their main use
is as subroutine libraries for linking.
* Menu:
* Archive Members::             Archive members as targets.
* Archive Update::              The implicit rule for archive member targets.
* Archive Suffix Rules::        You can write a special kind of suffix rule
                                  for updating archives.
File: make.info,  Node: Archive Members,  Next: Archive Update,  Up: Archives
Archive Members as Targets
==========================
   An individual member of an archive file can be used as a target or
dependency in `make'.  The archive file must already exist, but the
member need not exist.  You specify the member named MEMBER in archive
file ARCHIVE as follows:
     ARCHIVE(MEMBER)
This construct is available only in targets and dependencies, not in
commands!  Most programs that you might use in commands do not support
this syntax and cannot act directly on archive members.  Only `ar' and
other programs specifically designed to operate on archives can do so.
Therefore, valid commands to update an archive member target probably
must use `ar'.  For example, this rule says to create a member `hack.o'
in archive `foolib' by copying the file `hack.o':
     foolib(hack.o) : hack.o
             ar r foolib hack.o
   In fact, nearly all archive member targets are updated in just this
way and there is an implicit rule to do it for you.
   To specify several members in the same archive, you can write all the
member names together between the parentheses.  For example:
     foolib(hack.o kludge.o)
is equivalent to:
     foolib(hack.o) foolib(kludge.o)
   You can also use shell-style wildcards in an archive member
reference.  *Note Using Wildcard Characters in File Names: Wildcards.
For example, `foolib(*.o)' expands to all existing members of the
`foolib' archive whose names end in `.o'; perhaps `foolib(hack.o)
foolib(kludge.o)'.
File: make.info,  Node: Archive Update,  Next: Archive Suffix Rules,  Prev: Archive Members,  Up: Archives
Implicit Rule for Archive Member Targets
========================================
   Recall that a target that looks like `A(M)' stands for the member
named M in the archive file A.
   When `make' looks for an implicit rule for such a target, as a
special feature it considers implicit rules that match `(M)', as well as
those that match the actual target `A(M)'.
   This causes one special rule whose target is `(%)' to match.  This
rule updates the target `A(M)' by copying the file M into the archive.
For example, it will update the archive member target `foo.a(bar.o)' by
copying the *file* `bar.o' into the archive `foo.a' as a *member* named
`bar.o'.
   When this rule is chained with others, the result is very powerful.
Thus, `make "foo.a(bar.o)"' (the quotes are needed to protect the `('
and `)' from being interpreted specially by the shell) in the presence
of a file `bar.c' is enough to cause the following commands to be run,
even without a makefile:
     cc -c bar.c -o bar.o
     ar r foo.a bar.o
     rm -f bar.o
Here `make' has envisioned the file `bar.o' as an intermediate file.
*Note Chains of Implicit Rules: Chained Rules.
   Implicit rules such as this one are written using the automatic
variable `$%'.  *Note Automatic Variables: Automatic.
   An archive member name in an archive cannot contain a directory
name, but it may be useful in a makefile to pretend that it does.  If
you write an archive member target `foo.a(dir/file.o)', `make' will
perform automatic updating with this command:
     ar r foo.a dir/file.o
which has the effect of copying the file `dir/foo.o' into a member
named `foo.o'.  In connection with such usage, the automatic variables
`%D' and `%F' may be useful.
* Menu:
* Archive Symbols::             How to update archive symbol directories.
File: make.info,  Node: Archive Symbols,  Up: Archive Update
Updating Archive Symbol Directories
-----------------------------------
   An archive file that is used as a library usually contains a special
member named `__.SYMDEF' that contains a directory of the external
symbol names defined by all the other members.  After you update any
other members, you need to update `__.SYMDEF' so that it will summarize
the other members properly.  This is done by running the `ranlib'
program:
     ranlib ARCHIVEFILE
   Normally you would put this command in the rule for the archive file,
and make all the members of the archive file dependencies of that rule.
For example,
     libfoo.a: libfoo.a(x.o) libfoo.a(y.o) ...
             ranlib libfoo.a
The effect of this is to update archive members `x.o', `y.o', etc., and
then update the symbol directory member `__.SYMDEF' by running
`ranlib'.  The rules for updating the members are not shown here; most
likely you can omit them and use the implicit rule which copies files
into the archive, as described in the preceding section.
   This is not necessary when using the GNU `ar' program, which updates
the `__.SYMDEF' member automatically.
File: make.info,  Node: Archive Suffix Rules,  Prev: Archive Update,  Up: Archives
Suffix Rules for Archive Files
==============================
   You can write a special kind of suffix rule for dealing with archive
files.  *Note Suffix Rules::, for a full explanation of suffix rules.
Archive suffix rules are obsolete in GNU `make', because pattern rules
for archives are a more general mechanism (*note Archive Update::.).
But they are retained for compatibility with other `make's.
   To write a suffix rule for archives, you simply write a suffix rule
using the target suffix `.a' (the usual suffix for archive files).  For
example, here is the old-fashioned suffix rule to update a library
archive from C source files:
     .c.a:
             $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o
             $(AR) r $@ $*.o
             $(RM) $*.o
This works just as if you had written the pattern rule:
     (%.o): %.c
             $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o
             $(AR) r $@ $*.o
             $(RM) $*.o
   In fact, this is just what `make' does when it sees a suffix rule
with `.a' as the target suffix.  Any double-suffix rule `.X.a' is
converted to a pattern rule with the target pattern `(%.o)' and a
dependency pattern of `%.X'.
   Since you might want to use `.a' as the suffix for some other kind
of file, `make' also converts archive suffix rules to pattern rules in
the normal way (*note Suffix Rules::.).  Thus a double-suffix rule
`.X.a' produces two pattern rules: `(%.o): %.X' and `%.a: %.X'.
File: make.info,  Node: Features,  Next: Missing,  Prev: Archives,  Up: Top
Features of GNU `make'
**********************
   Here is a summary of the features of GNU `make', for comparison with
and credit to other versions of `make'.  We consider the features of
`make' in 4.2 BSD systems as a baseline.  If you are concerned with
writing portable makefiles, you should use only the features of `make'
*not* listed here or in *Note Missing::.
   Many features come from the version of `make' in System V.
   * The `VPATH' variable and its special meaning.  *Note Searching
     Directories for Dependencies: Directory Search.  This feature
     exists in System V `make', but is undocumented.  It is documented
     in 4.3 BSD `make' (which says it mimics System V's `VPATH'
     feature).
   * Included makefiles.  *Note Including Other Makefiles: Include.
     Allowing multiple files to be included with a single directive is
     a GNU extension.
   * Variables are read from and communicated via the environment.
     *Note Variables from the Environment: Environment.
   * Options passed through the variable `MAKEFLAGS' to recursive
     invocations of `make'.  *Note Communicating Options to a
     Sub-`make': Options/Recursion.
   * The automatic variable `$%' is set to the member name in an
     archive reference.  *Note Automatic Variables: Automatic.
   * The automatic variables `$@', `$*', `$<', `$%', and `$?' have
     corresponding forms like `$(@F)' and `$(@D)'.  We have generalized
     this to `$^' as an obvious extension.  *Note Automatic Variables:
     Automatic.
   * Substitution variable references.  *Note Basics of Variable
     References: Reference.
   * The command-line options `-b' and `-m', accepted and ignored.  In
     System V `make', these options actually do something.
   * Execution of recursive commands to run `make' via the variable
     `MAKE' even if `-n', `-q' or `-t' is specified.  *Note Recursive
     Use of `make': Recursion.
   * Support for suffix `.a' in suffix rules.  *Note Archive Suffix
     Rules::.  This feature is obsolete in GNU `make', because the
     general feature of rule chaining (*note Chains of Implicit Rules:
     Chained Rules.) allows one pattern rule for installing members in
     an archive (*note Archive Update::.) to be sufficient.
   * The arrangement of lines and backslash-newline combinations in
     commands is retained when the commands are printed, so they appear
     as they do in the makefile, except for the stripping of initial
     whitespace.
   The following features were inspired by various other versions of
`make'.  In some cases it is unclear exactly which versions inspired
which others.
   * Pattern rules using `%'.  This has been implemented in several
     versions of `make'.  We're not sure who invented it first, but
     it's been spread around a bit.  *Note Defining and Redefining
     Pattern Rules: Pattern Rules.
   * Rule chaining and implicit intermediate files.  This was
     implemented by Stu Feldman in his version of `make' for AT&T
     Eighth Edition Research Unix, and later by Andrew Hume of AT&T
     Bell Labs in his `mk' program (where he terms it "transitive
     closure").  We do not really know if we got this from either of
     them or thought it up ourselves at the same time.  *Note Chains of
     Implicit Rules: Chained Rules.
   * The automatic variable `$^' containing a list of all dependencies
     of the current target.  We did not invent this, but we have no
     idea who did.  *Note Automatic Variables: Automatic.
   * The "what if" flag (`-W' in GNU `make') was (as far as we know)
     invented by Andrew Hume in `mk'.  *Note Instead of Executing the
     Commands: Instead of Execution.
   * The concept of doing several things at once (parallelism) exists in
     many incarnations of `make' and similar programs, though not in the
     System V or BSD implementations.  *Note Command Execution:
     Execution.
   * Modified variable references using pattern substitution come from
     SunOS 4.  *Note Basics of Variable References: Reference.  This
     functionality was provided in GNU `make' by the `patsubst'
     function before the alternate syntax was implemented for
     compatibility with SunOS 4.  It is not altogether clear who
     inspired whom, since GNU `make' had `patsubst' before SunOS 4 was
     released.
   * The special significance of `+' characters preceding command lines
     (*note Instead of Executing the Commands: Instead of Execution.) is
     mandated by `IEEE Standard 1003.2-1992' (POSIX.2).
   * The `+=' syntax to append to the value of a variable comes from
     SunOS 4 `make'.  *Note Appending More Text to Variables: Appending.
   * The syntax `ARCHIVE(MEM1 MEM2...)' to list multiple members in a
     single archive file comes from SunOS 4 `make'.  *Note Archive
     Members::.
   * The `-include' directive to include makefiles with no error for a
     nonexistent file comes from SunOS 4 `make'.  (But note that SunOS 4
     `make' does not allow multiple makefiles to be specified in one
     `-include' directive.)
   The remaining features are inventions new in GNU `make':
   * Use the `-v' or `--version' option to print version and copyright
     information.
   * Use the `-h' or `--help' option to summarize the options to `make'.
   * Simply-expanded variables.  *Note The Two Flavors of Variables:
     Flavors.
   * Pass command-line variable assignments automatically through the
     variable `MAKE' to recursive `make' invocations.  *Note Recursive
     Use of `make': Recursion.
   * Use the `-C' or `--directory' command option to change directory.
     *Note Summary of Options: Options Summary.
   * Make verbatim variable definitions with `define'.  *Note Defining
     Variables Verbatim: Defining.
   * Declare phony targets with the special target `.PHONY'.
     Andrew Hume of AT&T Bell Labs implemented a similar feature with a
     different syntax in his `mk' program.  This seems to be a case of
     parallel discovery.  *Note Phony Targets: Phony Targets.
   * Manipulate text by calling functions.  *Note Functions for
     Transforming Text: Functions.
   * Use the `-o' or `--old-file' option to pretend a file's
     modification-time is old.  *Note Avoiding Recompilation of Some
     Files: Avoiding Compilation.
   * Conditional execution.
     This feature has been implemented numerous times in various
     versions of `make'; it seems a natural extension derived from the
     features of the C preprocessor and similar macro languages and is
     not a revolutionary concept.  *Note Conditional Parts of
     Makefiles: Conditionals.
   * Specify a search path for included makefiles.  *Note Including
     Other Makefiles: Include.
   * Specify extra makefiles to read with an environment variable.
     *Note The Variable `MAKEFILES': MAKEFILES Variable.
   * Strip leading sequences of `./' from file names, so that `./FILE'
     and `FILE' are considered to be the same file.
   * Use a special search method for library dependencies written in the
     form `-lNAME'.  *Note Directory Search for Link Libraries:
     Libraries/Search.
   * Allow suffixes for suffix rules (*note Old-Fashioned Suffix Rules:
     Suffix Rules.) to contain any characters.  In other versions of
     `make', they must begin with `.' and not contain any `/'
     characters.
   * Keep track of the current level of `make' recursion using the
     variable `MAKELEVEL'.  *Note Recursive Use of `make': Recursion.
   * Specify static pattern rules.  *Note Static Pattern Rules: Static
     Pattern.
   * Provide selective `vpath' search.  *Note Searching Directories for
     Dependencies: Directory Search.
   * Provide computed variable references.  *Note Basics of Variable
     References: Reference.
   * Update makefiles.  *Note How Makefiles Are Remade: Remaking
     Makefiles.  System V `make' has a very, very limited form of this
     functionality in that it will check out SCCS files for makefiles.
   * Various new built-in implicit rules.  *Note Catalogue of Implicit
     Rules: Catalogue of Rules.
   * The built-in variable `MAKE_VERSION' gives the version number of
     `make'.
File: make.info,  Node: Missing,  Next: Makefile Conventions,  Prev: Features,  Up: Top
Incompatibilities and Missing Features
**************************************
   The `make' programs in various other systems support a few features
that are not implemented in GNU `make'.  The POSIX.2 standard (`IEEE
Standard 1003.2-1992') which specifies `make' does not require any of
these features.
   * A target of the form `FILE((ENTRY))' stands for a member of
     archive file FILE.  The member is chosen, not by name, but by
     being an object file which defines the linker symbol ENTRY.
     This feature was not put into GNU `make' because of the
     nonmodularity of putting knowledge into `make' of the internal
     format of archive file symbol tables.  *Note Updating Archive
     Symbol Directories: Archive Symbols.
   * Suffixes (used in suffix rules) that end with the character `~'
     have a special meaning to System V `make'; they refer to the SCCS
     file that corresponds to the file one would get without the `~'.
     For example, the suffix rule `.c~.o' would make the file `N.o' from
     the SCCS file `s.N.c'.  For complete coverage, a whole series of
     such suffix rules is required.  *Note Old-Fashioned Suffix Rules:
     Suffix Rules.
     In GNU `make', this entire series of cases is handled by two
     pattern rules for extraction from SCCS, in combination with the
     general feature of rule chaining.  *Note Chains of Implicit Rules:
     Chained Rules.
   * In System V `make', the string `$$@' has the strange meaning that,
     in the dependencies of a rule with multiple targets, it stands for
     the particular target that is being processed.
     This is not defined in GNU `make' because `$$' should always stand
     for an ordinary `$'.
     It is possible to get this functionality through the use of static
     pattern rules (*note Static Pattern Rules: Static Pattern.).  The
     System V `make' rule:
          $(targets): $$@.o lib.a
     can be replaced with the GNU `make' static pattern rule:
          $(targets): %: %.o lib.a
   * In System V and 4.3 BSD `make', files found by `VPATH' search
     (*note Searching Directories for Dependencies: Directory Search.)
     have their names changed inside command strings.  We feel it is
     much cleaner to always use automatic variables and thus make this
     feature obsolete.
   * In some Unix `make's, the automatic variable `$*' appearing in the
     dependencies of a rule has the amazingly strange "feature" of
     expanding to the full name of the *target of that rule*.  We cannot
     imagine what went on in the minds of Unix `make' developers to do
     this; it is utterly inconsistent with the normal definition of
     `$*'.
   * In some Unix `make's, implicit rule search (*note Using Implicit
     Rules: Implicit Rules.) is apparently done for *all* targets, not
     just those without commands.  This means you can do:
          foo.o:
                  cc -c foo.c
     and Unix `make' will intuit that `foo.o' depends on `foo.c'.
     We feel that such usage is broken.  The dependency properties of
     `make' are well-defined (for GNU `make', at least), and doing such
     a thing simply does not fit the model.
   * GNU `make' does not include any built-in implicit rules for
     compiling or preprocessing EFL programs.  If we hear of anyone who
     is using EFL, we will gladly add them.
   * It appears that in SVR4 `make', a suffix rule can be specified with
     no commands, and it is treated as if it had empty commands (*note
     Empty Commands::.).  For example:
          .c.a:
     will override the built-in `.c.a' suffix rule.
     We feel that it is cleaner for a rule without commands to always
     simply add to the dependency list for the target.  The above
     example can be easily rewritten to get the desired behavior in GNU
     `make':
          .c.a: ;
   * Some versions of `make' invoke the shell with the `-e' flag,
     except under `-k' (*note Testing the Compilation of a Program:
     Testing.).  The `-e' flag tells the shell to exit as soon as any
     program it runs returns a nonzero status.  We feel it is cleaner to
     write each shell command line to stand on its own and not require
     this special treatment.
File: make.info,  Node: Makefile Conventions,  Next: Quick Reference,  Prev: Missing,  Up: Top
Makefile Conventions
********************
   This chapter describes conventions for writing the Makefiles for GNU
programs.
* Menu:
* Makefile Basics::
* Utilities in Makefiles::
* Standard Targets::
* Command Variables::
* Directory Variables::
File: make.info,  Node: Makefile Basics,  Next: Utilities in Makefiles,  Up: Makefile Conventions
General Conventions for Makefiles
=================================
   Every Makefile should contain this line:
     SHELL = /bin/sh
to avoid trouble on systems where the `SHELL' variable might be
inherited from the environment.  (This is never a problem with GNU
`make'.)
   Don't assume that `.' is in the path for command execution.  When
you need to run programs that are a part of your package during the
make, please make sure that it uses `./' if the program is built as
part of the make or `$(srcdir)/' if the file is an unchanging part of
the source code.  Without one of these prefixes, the current search
path is used.
   The distinction between `./' and `$(srcdir)/' is important when
using the `--srcdir' option to `configure'.  A rule of the form:
     foo.1 : foo.man sedscript
             sed -e sedscript foo.man > foo.1
will fail when the current directory is not the source directory,
because `foo.man' and `sedscript' are not in the current directory.
   When using GNU `make', relying on `VPATH' to find the source file
will work in the case where there is a single dependency file, since
the `make' automatic variable `$<' will represent the source file
wherever it is.  (Many versions of `make' set `$<' only in implicit
rules.)  A makefile target like
     foo.o : bar.c
             $(CC) -I. -I$(srcdir) $(CFLAGS) -c bar.c -o foo.o
should instead be written as
     foo.o : bar.c
             $(CC) $(CFLAGS) $< -o $@
in order to allow `VPATH' to work correctly.  When the target has
multiple dependencies, using an explicit `$(srcdir)' is the easiest way
to make the rule work well.  For example, the target above for `foo.1'
is best written as:
     foo.1 : foo.man sedscript
             sed -s $(srcdir)/sedscript $(srcdir)/foo.man > foo.1
File: make.info,  Node: Utilities in Makefiles,  Next: Standard Targets,  Prev: Makefile Basics,  Up: Makefile Conventions
Utilities in Makefiles
======================
   Write the Makefile commands (and any shell scripts, such as
`configure') to run in `sh', not in `csh'.  Don't use any special
features of `ksh' or `bash'.
   The `configure' script and the Makefile rules for building and
installation should not use any utilities directly except these:
     cat cmp cp echo egrep expr grep
     ln mkdir mv pwd rm rmdir sed test touch
   Stick to the generally supported options for these programs.  For
example, don't use `mkdir -p', convenient as it may be, because most
systems don't support it.
   The Makefile rules for building and installation can also use
compilers and related programs, but should do so via `make' variables
so that the user can substitute alternatives.  Here are some of the
programs we mean:
     ar bison cc flex install ld lex
     make makeinfo ranlib texi2dvi yacc
   When you use `ranlib', you should test whether it exists, and run it
only if it exists, so that the distribution will work on systems that
don't have `ranlib'.
   If you use symbolic links, you should implement a fallback for
systems that don't have symbolic links.
   It is ok to use other utilities in Makefile portions (or scripts)
intended only for particular systems where you know those utilities to
exist.
File: make.info,  Node: Standard Targets,  Next: Command Variables,  Prev: Utilities in Makefiles,  Up: Makefile Conventions
Standard Targets for Users
==========================
   All GNU programs should have the following targets in their
Makefiles:
`all'
     Compile the entire program.  This should be the default target.
     This target need not rebuild any documentation files; Info files
     should normally be included in the distribution, and DVI files
     should be made only when explicitly asked for.
`install'
     Compile the program and copy the executables, libraries, and so on
     to the file names where they should reside for actual use.  If
     there is a simple test to verify that a program is properly
     installed, this target should run that test.
     The commands should create all the directories in which files are
     to be installed, if they don't already exist.  This includes the
     directories specified as the values of the variables `prefix' and
     `exec_prefix', as well as all subdirectories that are needed.  One
     way to do this is by means of an `installdirs' target as described
     below.
     Use `-' before any command for installing a man page, so that
     `make' will ignore any errors.  This is in case there are systems
     that don't have the Unix man page documentation system installed.
     The way to install Info files is to copy them into `$(infodir)'
     with `$(INSTALL_DATA)' (*note Command Variables::.), and then run
     the `install-info' program if it is present.  `install-info' is a
     script that edits the Info `dir' file to add or update the menu
     entry for the given Info file; it will be part of the Texinfo
     package.  Here is a sample rule to install an Info file:
          $(infodir)/foo.info: foo.info
          # There may be a newer info file in . than in srcdir.
                  -if test -f foo.info; then d=.; \
                   else d=$(srcdir); fi; \
                  $(INSTALL_DATA) $$d/foo.info $@; \
          # Run install-info only if it exists.
          # Use `if' instead of just prepending `-' to the
          # line so we notice real errors from install-info.
          # We use `$(SHELL) -c' because some shells do not
          # fail gracefully when there is an unknown command.
                  if $(SHELL) -c 'install-info --version' \
                     >/dev/null 2>&1; then \
                    install-info --infodir=$(infodir) $$d/foo.info; \
                  else true; fi
`uninstall'
     Delete all the installed files that the `install' target would
     create (but not the noninstalled files such as `make all' would
     create).
`clean'
     Delete all files from the current directory that are normally
     created by building the program.  Don't delete the files that
     record the configuration.  Also preserve files that could be made
     by building, but normally aren't because the distribution comes
     with them.
     Delete `.dvi' files here if they are not part of the distribution.
`distclean'
     Delete all files from the current directory that are created by
     configuring or building the program.  If you have unpacked the
     source and built the program without creating any other files,
     `make distclean' should leave only the files that were in the
     distribution.
`mostlyclean'
     Like `clean', but may refrain from deleting a few files that people
     normally don't want to recompile.  For example, the `mostlyclean'
     target for GCC does not delete `libgcc.a', because recompiling it
     is rarely necessary and takes a lot of time.
`realclean'
     Delete everything from the current directory that can be
     reconstructed with this Makefile.  This typically includes
     everything deleted by `distclean', plus more: C source files
     produced by Bison, tags tables, Info files, and so on.
     One exception, however: `make realclean' should not delete
     `configure' even if `configure' can be remade using a rule in the
     Makefile.  More generally, `make realclean' should not delete
     anything that needs to exist in order to run `configure' and then
     begin to build the program.
`TAGS'
     Update a tags table for this program.
`info'
     Generate any Info files needed.  The best way to write the rules
     is as follows:
          info: foo.info

          foo.info: foo.texi chap1.texi chap2.texi
                  $(MAKEINFO) $(srcdir)/foo.texi
     You must define the variable `MAKEINFO' in the Makefile.  It should
     run the `makeinfo' program, which is part of the Texinfo
     distribution.
`dvi'
     Generate DVI files for all TeXinfo documentation.  For example:
          dvi: foo.dvi

          foo.dvi: foo.texi chap1.texi chap2.texi
                  $(TEXI2DVI) $(srcdir)/foo.texi
     You must define the variable `TEXI2DVI' in the Makefile.  It should
     run the program `texi2dvi', which is part of the Texinfo
     distribution.  Alternatively, write just the dependencies, and
     allow GNU Make to provide the command.
`dist'
     Create a distribution tar file for this program.  The tar file
     should be set up so that the file names in the tar file start with
     a subdirectory name which is the name of the package it is a
     distribution for.  This name can include the version number.
     For example, the distribution tar file of GCC version 1.40 unpacks
     into a subdirectory named `gcc-1.40'.
     The easiest way to do this is to create a subdirectory
     appropriately named, use `ln' or `cp' to install the proper files
     in it, and then `tar' that subdirectory.
     The `dist' target should explicitly depend on all non-source files
     that are in the distribution, to make sure they are up to date in
     the distribution.  *Note Making Releases: (standards)Releases.
`check'
     Perform self-tests (if any).  The user must build the program
     before running the tests, but need not install the program; you
     should write the self-tests so that they work when the program is
     built but not installed.
   The following targets are suggested as conventional names, for
programs in which they are useful.
`installcheck'
     Perform installation tests (if any).  The user must build and
     install the program before running the tests.  You should not
     assume that `$(bindir)' is in the search path.
`installdirs'
     It's useful to add a target named `installdirs' to create the
     directories where files are installed, and their parent
     directories.  There is a script called `mkinstalldirs' which is
     convenient for this; find it in the Texinfo package.You can use a
     rule like this:
          # Make sure all installation directories (e.g. $(bindir))
          # actually exist by making them if necessary.
          installdirs: mkinstalldirs
                  $(srcdir)/mkinstalldirs $(bindir) $(datadir) \
                                          $(libdir) $(infodir) \
                                          $(mandir)
File: make.info,  Node: Command Variables,  Next: Directory Variables,  Prev: Standard Targets,  Up: Makefile Conventions
Variables for Specifying Commands
=================================
   Makefiles should provide variables for overriding certain commands,
options, and so on.
   In particular, you should run most utility programs via variables.
Thus, if you use Bison, have a variable named `BISON' whose default
value is set with `BISON = bison', and refer to it with `$(BISON)'
whenever you need to use Bison.
   File management utilities such as `ln', `rm', `mv', and so on, need
not be referred to through variables in this way, since users don't
need to replace them with other programs.
   Each program-name variable should come with an options variable that
is used to supply options to the program.  Append `FLAGS' to the
program-name variable name to get the options variable name--for
example, `BISONFLAGS'.  (The name `CFLAGS' is an exception to this
rule, but we keep it because it is standard.)  Use `CPPFLAGS' in any
compilation command that runs the preprocessor, and use `LDFLAGS' in
any compilation command that does linking as well as in any direct use
of `ld'.
   If there are C compiler options that *must* be used for proper
compilation of certain files, do not include them in `CFLAGS'.  Users
expect to be able to specify `CFLAGS' freely themselves.  Instead,
arrange to pass the necessary options to the C compiler independently
of `CFLAGS', by writing them explicitly in the compilation commands or
by defining an implicit rule, like this:
     CFLAGS = -g
     ALL_CFLAGS = -I. $(CFLAGS)
     .c.o:
             $(CC) -c $(CPPFLAGS) $(ALL_CFLAGS) $<
   Do include the `-g' option in `CFLAGS', because that is not
*required* for proper compilation.  You can consider it a default that
is only recommended.  If the package is set up so that it is compiled
with GCC by default, then you might as well include `-O' in the default
value of `CFLAGS' as well.
   Put `CFLAGS' last in the compilation command, after other variables
containing compiler options, so the user can use `CFLAGS' to override
the others.
   Every Makefile should define the variable `INSTALL', which is the
basic command for installing a file into the system.
   Every Makefile should also define the variables `INSTALL_PROGRAM'
and `INSTALL_DATA'.  (The default for each of these should be
`$(INSTALL)'.)  Then it should use those variables as the commands for
actual installation, for executables and nonexecutables respectively.
Use these variables as follows:
     $(INSTALL_PROGRAM) foo $(bindir)/foo
     $(INSTALL_DATA) libfoo.a $(libdir)/libfoo.a
Always use a file name, not a directory name, as the second argument of
the installation commands.  Use a separate command for each file to be
installed.
File: make.info,  Node: Directory Variables,  Prev: Command Variables,  Up: Makefile Conventions
Variables for Installation Directories
======================================
   Installation directories should always be named by variables, so it
is easy to install in a nonstandard place.  The standard names for these
variables are:
`prefix'
     A prefix used in constructing the default values of the variables
     listed below.  The default value of `prefix' should be `/usr/local'
     (at least for now).
`exec_prefix'
     A prefix used in constructing the default values of some of the
     variables listed below.  The default value of `exec_prefix' should
     be `$(prefix)'.
     Generally, `$(exec_prefix)' is used for directories that contain
     machine-specific files (such as executables and subroutine
     libraries), while `$(prefix)' is used directly for other
     directories.
`bindir'
     The directory for installing executable programs that users can
     run.  This should normally be `/usr/local/bin', but write it as
     `$(exec_prefix)/bin'.
`libdir'
     The directory for installing executable files to be run by the
     program rather than by users.  Object files and libraries of
     object code should also go in this directory.  The idea is that
     this directory is used for files that pertain to a specific
     machine architecture, but need not be in the path for commands.
     The value of `libdir' should normally be `/usr/local/lib', but
     write it as `$(exec_prefix)/lib'.
`datadir'
     The directory for installing read-only data files which the
     programs refer to while they run.  This directory is used for
     files which are independent of the type of machine being used.
     This should normally be `/usr/local/lib', but write it as
     `$(prefix)/lib'.
`statedir'
     The directory for installing data files which the programs modify
     while they run.  These files should be independent of the type of
     machine being used, and it should be possible to share them among
     machines at a network installation.  This should normally be
     `/usr/local/lib', but write it as `$(prefix)/lib'.
`includedir'
     The directory for installing header files to be included by user
     programs with the C `#include' preprocessor directive.  This
     should normally be `/usr/local/include', but write it as
     `$(prefix)/include'.
     Most compilers other than GCC do not look for header files in
     `/usr/local/include'.  So installing the header files this way is
     only useful with GCC.  Sometimes this is not a problem because some
     libraries are only really intended to work with GCC.  But some
     libraries are intended to work with other compilers.  They should
     install their header files in two places, one specified by
     `includedir' and one specified by `oldincludedir'.
`oldincludedir'
     The directory for installing `#include' header files for use with
     compilers other than GCC.  This should normally be `/usr/include'.
     The Makefile commands should check whether the value of
     `oldincludedir' is empty.  If it is, they should not try to use
     it; they should cancel the second installation of the header files.
     A package should not replace an existing header in this directory
     unless the header came from the same package.  Thus, if your Foo
     package provides a header file `foo.h', then it should install the
     header file in the `oldincludedir' directory if either (1) there
     is no `foo.h' there or (2) the `foo.h' that exists came from the
     Foo package.
     To tell whether `foo.h' came from the Foo package, put a magic
     string in the file--part of a comment--and grep for that string.
`mandir'
     The directory for installing the man pages (if any) for this
     package.  It should include the suffix for the proper section of
     the manual--usually `1' for a utility.  It will normally be
     `/usr/local/man/man1', but you should write it as
     `$(prefix)/man/man1'.
`man1dir'
     The directory for installing section 1 man pages.
`man2dir'
     The directory for installing section 2 man pages.
`...'
     Use these names instead of `mandir' if the package needs to
     install man pages in more than one section of the manual.
     *Don't make the primary documentation for any GNU software be a
     man page.  Write a manual in Texinfo instead.  Man pages are just
     for the sake of people running GNU software on Unix, which is a
     secondary application only.*
`manext'
     The file name extension for the installed man page.  This should
     contain a period followed by the appropriate digit; it should
     normally be `.1'.
`man1ext'
     The file name extension for installed section 1 man pages.
`man2ext'
     The file name extension for installed section 2 man pages.
`...'
     Use these names instead of `manext' if the package needs to
     install man pages in more than one section of the manual.
`infodir'
     The directory for installing the Info files for this package.  By
     default, it should be `/usr/local/info', but it should be written
     as `$(prefix)/info'.
`srcdir'
     The directory for the sources being compiled.  The value of this
     variable is normally inserted by the `configure' shell script.
   For example:
     # Common prefix for installation directories.
     # NOTE: This directory must exist when you start the install.
     prefix = /usr/local
     exec_prefix = $(prefix)
     # Where to put the executable for the command `gcc'.
     bindir = $(exec_prefix)/bin
     # Where to put the directories used by the compiler.
     libdir = $(exec_prefix)/lib
     # Where to put the Info files.
     infodir = $(prefix)/info
   If your program installs a large number of files into one of the
standard user-specified directories, it might be useful to group them
into a subdirectory particular to that program.  If you do this, you
should write the `install' rule to create these subdirectories.
   Do not expect the user to include the subdirectory name in the value
of any of the variables listed above.  The idea of having a uniform set
of variable names for installation directories is to enable the user to
specify the exact same values for several different GNU packages.  In
order for this to be useful, all the packages must be designed so that
they will work sensibly when the user does so.