make(1)

make -- maintain, update, and regenerate groups of programs

Synopsis

make [-f makefile] [-BeiknpPqrstuw] [names]

Description

make allows the programmer to maintain, update, and regenerate groups of computer programs. make executes commands in makefile to update one or more target names (names are typically programs). If the -f option is not present, then makefile, Makefile, and the Source Code Control System (SCCS) files s.makefile, and s.Makefile are tried in order. If makefile is -, the standard input is taken. More than one -f makefile argument pair may appear.

make updates a target only if its dependents are newer than the target. All prerequisite files of a target are added recursively to the list of targets. Missing files are deemed to be outdated.

The following list of directives can be included in makefiles to modify the behavior of make. They are used in makefiles as if they were targets:

.DEFAULT:: If a file must be made but there are no explicit commands or relevant built-in rules, the commands associated with the name .DEFAULT are used if it exists.
.IGNORE:: Same effect as the -i option.
.MUTEX:: Serialize the updating of specified targets (see the ``Parallel make'' subsection, below).
.PRECIOUS:: Dependents of the .PRECIOUS entry will not be removed when quit or interrupt are pressed.
.SILENT:: Same effect as the -s option.

The options for make are listed below:

-B: Arrange the output of parallel make in appropriate blocks for readability.
-e: Environment variables override assignments within makefiles.
-f makefile: Description filename (makefile is assumed to be the name of a description file).
-i: Ignore error codes returned by invoked commands.
-k: Abandon work on the current entry if it fails, but continue on other branches that do not depend on that entry.
-n: No execute mode. Print commands, but do not execute them. Even command lines beginning with an ``@'' are printed.
-p: Print out the complete set of macro definitions and target descriptions.
-P: Update in parallel more than one target at a time. The number of targets updated concurrently is determined by the environment variable PARALLEL and the presence of .MUTEX directives in makefiles.
-q: Question. make returns a zero or non-zero status code depending on whether or not the target file has been updated.
-r: Do not use the built-in rules.
-s: Silent mode. Do not print command lines before executing.
-t: Touch the target files (causing them to be updated) rather than issue the usual commands.
-u: Unconditionally make the target, ignoring all timestamps.
-w: Suppress warning messages. Fatal messages will not be affected.

Creating the makefile

The makefile invoked with the -f option (or accessed by default) is a carefully structured file of explicit instructions for updating and regenerating programs, and contains a sequence of entries that specify dependencies. The first line of an entry is a blank-separated, non-null list of targets, then a ``:'', then a (possibly null) list of prerequisite files or dependencies. Text following a ``;'' and all following lines that begin with a tab are shell commands to be executed to update the target. The first non-empty line that does not begin with a tab or ``#'' begins a new dependency or macro definition. Shell commands may be continued across lines with a backslash-new-line (``\'' new-line) sequence. Everything printed by make (except the initial tab) is passed directly to the shell as is. Thus,

   echo a\
   b

will produce

ab

exactly the same as the shell would.

Sharp (#) and new-line surround comments including contained ``\'' new-line sequences.

The following makefile says that pgm depends on two files a.o and b.o, and that they in turn depend on their corresponding source files (a.c and b.c) and a common file incl.h:

   pgm: a.o b.o
   	cc a.o b.o -o pgm
   a.o: incl.h a.c
   	cc -c a.c
   b.o: incl.h b.c
   	cc -c b.c

Command lines are executed one at a time, each by its own shell. The SHELL environment variable can be used to specify which shell make should use to execute commands. The default is /usr/bin/sh. The first one or two characters in a command can be the following: ``@'', ``-'', ``@-'', or ``-@''. If ``@'' is present, printing of the command is suppressed. If ``-'' is present, make ignores an error. A line is printed when it is executed unless the -s option is present, or the entry .SILENT: is included in the makefile, or unless the initial character sequence contains a ``@''. The -n option specifies printing without execution; however, if the command line has the string ``$(MAKE)'' in it, the line is always executed (see the discussion of the MAKEFLAGS macro in the ``Environment'' section). The -t (touch) option updates the modified date of a file without executing any commands.

Commands returning non-zero status normally terminate make. If the -i option is present, if the entry .IGNORE: is included in the makefile, or if the initial character sequence of the command contains -, the error is ignored. If the -k option is present, work is abandoned on the current entry, but continues on other branches that do not depend on that entry.

Interrupt and quit cause the target to be deleted unless the target is a dependent of the directive .PRECIOUS.

Parallel make

If make is invoked with the -P option, it tries to build more than one target at a time, in parallel. (This is done by using the standard UNIX system process mechanism which enables multiple processes to run simultaneously.) For the makefile shown in the example in the previous section, it would create processes to build a.o and b.o in parallel. After these processes were complete, it would build pgm.

The number of targets make will try to build in parallel is determined by the value of the environment variable PARALLEL. If -P is invoked, but PARALLEL is not set, then make will try to build no more than two targets in parallel.

You can use the .MUTEX directive to serialize the updating of some specified targets. This is useful when two or more targets modify a common output file, such as when inserting modules into an archive or when creating an intermediate file with the same name, as is done by lex and yacc. If the makefile in the previous section contained a .MUTEX directive of the form

   .MUTEX: a.o b.o

it would prevent make from building a.o and b.o in parallel.

Environment

The environment is read by make. All variables are assumed to be macro definitions and are processed as such. The environment variables are processed before any makefile and after the internal rules; thus, macro assignments in a makefile override environment variables. The -e option causes the environment to override the macro assignments in a makefile. Suffixes and their associated rules in the makefile will override any identical suffixes in the built-in rules.

The MAKEFLAGS environment variable is processed by make as containing any legal input option (except -f, -p and -r) defined for the command line. Further, upon invocation, make invents the variable if it is not in the environment, puts the current options into it, and passes it on to invocations of commands. Thus, MAKEFLAGS always contains the current input options. This feature proves very useful for ``super-makes''. In fact, as noted above, when the -n option is used, the command $(MAKE) is executed anyway; hence, one can perform a make -n recursively on a whole software system to see what would have been executed. This result is possible because the -n is put in MAKEFLAGS and passed to further invocations of $(MAKE). This usage is one way of debugging all of the makefiles for a software project without actually doing anything.

Include files

If the string include appears as the first seven letters of a line in a makefile, and is followed by a blank or a tab, the rest of the line is assumed to be a filename and will be read by the current invocation, after substituting for any macros.

Macros

Entries of the form ``string1 = string2'' are macro definitions. string2 is defined as all characters up to a comment character or an unescaped new-line. Subsequent appearances of ``$(string1[:subst1=[subst2]])'' are replaced by string2. The parentheses are optional if a single-character macro name is used and there is no substitute sequence. The macro ``$$'' is replaced by the single character ``$''. The optional ``:subst1=subst2'' is a substitute sequence. If it is specified, all non-overlapping occurrences of subst1 in the named macro are replaced by subst2. Strings (for the purposes of this type of substitution) are delimited by blanks, tabs, new-line characters, and beginnings of lines. An example of the use of the substitute sequence is shown in the ``Libraries'' section.

Internal macros

There are five internally maintained macros that are useful for writing rules for building targets.

$

The macro $ stands for the filename part of the current dependent with the suffix deleted. It is evaluated only for inference rules.

$@

The $@ macro stands for the full target name of the current target. It is evaluated only for explicitly named dependencies.

$<

The $< macro is only evaluated for inference rules or the .DEFAULT rule. It is the module that is outdated with respect to the target (the manufactured dependent file name). Thus, in the ``.c.o'' rule, the $< macro would evaluate to the .c file. An example for making optimized .o files from .c files is:

.c.o:
cc -c -O $

or alternatively:

.c.o:
cc -c -O $<

$?

The $? macro is evaluated when explicit rules from the makefile are evaluated. It is the list of prerequisites that are outdated with respect to the target, and essentially those modules that must be rebuilt.

$%

The $% macro is only evaluated when the target is an archive library member of the form ``lib(file.o)''. In this case, $@ evaluates to ``lib'' and $% evaluates to the library member, file.o.

Four of the five macros can have alternative forms. When an upper case ``D'' or ``F'' is appended to any of the four macros, the meaning is changed to ``directory part'' for ``D'' and ``file part'' for ``F''. Thus, $(@D) refers to the directory part of the string ``$@''. If there is no directory part, ./ is generated. The only macro excluded from this alternative form is $?.

Suffixes

Certain names (for instance, those ending with .o) have inferable prerequisites such as .c, .s, and so on. If no update commands for such a file appear in the makefile, and if an inferable prerequisite exists, that prerequisite is compiled to make the target. In this case, make has inference rules that allow building files from other files by examining the suffixes and determining an appropriate inference rule to use. The current default inference rules are:

.c .c~ .f .f~ .s .s~ .sh .sh~ .C .C~

.c.a .c.o .c~.a .c~.c .c~.o .f.a .f.o .f~.a .f~.f .f~.o

.h~.h .l.c .l.o .l~.c .l~.l .l~.o .s.a .s.o .s~.a .s~.o

.s~.s .sh~.sh .y.c .y.o .y~.c .y~.o .y~.y .C.a .C.o .C~.a

.C~.C .C~.o .L.C .L.o .L~.C .L~.L .L~.o .Y.C .Y.o .Y~.C

.Y~.o .Y~.Y

The internal rules for make are contained in the source file rules.c for the make program. These rules can be locally modified. To print out the rules compiled into the make on any machine in a form suitable for recompilation, the following command is used:

make -pf - 2>/dev/null </dev/null

A tilde in the above rules refers to an SCCS file (see sccsfile(4)). Thus, the rule ``.c~.o'' would transform an SCCS C source file into an object file (.o). Because the s. of the SCCS files is a prefix, it is incompatible with the make suffix point of view. Hence, the tilde is a way of changing any file reference into an SCCS file reference.

A rule with only one suffix (for example, ``.c:'') is the definition of how to build x from x.c. In effect, the other suffix is null. This feature is useful for building targets from only one source file, for example, shell procedures and simple C programs.

Additional suffixes are given as the dependency list for .SUFFIXES. Order is significant: the first possible name for which both a file and a rule exist is inferred as a prerequisite. The default list is:

.SUFFIXES: .o .c .c~ .y .y~ .l .l~ .s .s~ .sh .sh~ .h .h~ .f .f~
.C .C~ .Y .Y~ .L .L~

Here again, the above command for printing the internal rules will display the list of suffixes implemented on the current machine. Multiple suffix lists accumulate; .SUFFIXES: with no dependencies clears the list of suffixes.

Inference rules

The first example can be done more briefly:

   pgm: a.o b.o
   	cc a.o b.o -o pgm
   a.o b.o: incl.h

This abbreviation is possible because make has a set of internal rules for building files. The user may add rules to this list by simply putting them in the makefile.

Certain macros are used by the default inference rules to permit the inclusion of optional matter in any resulting commands. For example, CFLAGS, LFLAGS, and YFLAGS are used for compiler options to cc(1), lex(1), and yacc(1), respectively. Again, the previous method for examining the current rules is recommended.

The inference of prerequisites can be controlled. The rule to create a file with suffix .o from a file with suffix .c is specified as an entry with ``.c.o:'' as the target and no dependents. Shell commands associated with the target define the rule for making a .o file from a .c file. Any target that has no slashes in it and starts with a dot is identified as a rule and not a true target.

Libraries

If a target or dependency name contains parentheses, it is assumed to be an archive library, the string within parentheses referring to a member within the library. Thus, ``lib(file.o)'' and ``$(LIB)(file.o)'' both refer to an archive library that contains file.o. (This example assumes the LIB macro has been previously defined.) The expression $(LIB)(file1.o file2.o) is not legal. Rules pertaining to archive libraries have the form ``.XX.a'' where the XX is the suffix from which the archive member is to be made. Note that the current implementation requires the XX to be different from the suffix of the archive member. Thus, one cannot have ``lib(file.o)'' depend upon file.o explicitly. The most common use of the archive interface follows. Here, we assume the source files are all C type source:

   lib:     lib(file1.o) lib(file2.o) lib(file3.o)
            @echo lib is now up-to-date
   .c.a:
            $(CC) -c $(CFLAGS) $<
            $(AR) $(ARFLAGS) $@ $(<F:.c=.o)
            rm -f $(<F:.c=.o)

In fact, the ``.c.a'' rule listed above is built into make and is unnecessary in this example. A more interesting, but more limited example of an archive library maintenance construction follows:

   lib:     lib(file1.o) lib(file2.o) lib(file3.o)
            $(CC) -c $(CFLAGS) $(?:.o=.c)
            $(AR) $(ARFLAGS) lib $?
            rm $?
            @echo lib is now up-to-date
   .c.a:;

Here the substitution mode of the macro expansions is used. The ``$?'' list is defined to be the set of object filenames (inside lib) whose C source files are outdated. The substitution mode translates the .o to .c. (Unfortunately, one cannot as yet transform to .c~; however, this transformation may become possible in the future.) Also note the disabling of the ``.c.a:'' rule, which would have created each object file, one by one. This particular construct speeds up archive library maintenance considerably. This type of construct becomes very cumbersome if the archive library contains a mix of assembly programs and C programs.

Files

[Mm]akefile
s.[Mm]akefile
/usr/bin/sh
/usr/lib/locale/locale/LC_MESSAGES/uxepu: language-specific message file (see LANG in environ(5))

References

cc(1), cd(1), fprintf(3S), lex(1), sccsfile(4), sh(1), yacc(1)

Notices

Some commands return non-zero status inappropriately; use -i or the - command line prefix to overcome the difficulty.

Filenames with the characters ``='', ``:'', and ``@'' will not work. Commands that are directly executed by the shell, notably cd(1), are ineffectual across new-lines in make. The syntax ``lib(file1.o file2.o file3.o)'' is illegal. You cannot build ``lib(file.o)'' from file.o.

.c	.c~	.f	.f~	.s	.s~	.sh	.sh~	.C	.C~
.c.a	.c.o	.c~.a	.c~.c	.c~.o	.f.a	.f.o	.f~.a	.f~.f	.f~.o
.h~.h	.l.c	.l.o	.l~.c	.l~.l	.l~.o	.s.a	.s.o	.s~.a	.s~.o
.s~.s	.sh~.sh	.y.c	.y.o	.y~.c	.y~.o	.y~.y	.C.a	.C.o	.C~.a
.C~.C	.C~.o	.L.C	.L.o	.L~.C	.L~.L	.L~.o	.Y.C	.Y.o	.Y~.C
.Y~.o	.Y~.Y