make(1) USER COMMANDS make(1)
NAME
make - maintain, update, and regenerate groups of programs
SYNOPSIS
make [-f makefile] [-eiknpqrst] [names]
DESCRIPTION
make allows the programmer to maintain, update, and regen-
erate 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deemed to be outdated.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 four directives can be included in
makefile to extend the options provided by make. They are
used in makefile 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.
.PRECIOUS: Dependents of the .PRECIOUS entry will not
be removed when quit or interrupt are hit.
.SILENT: Same effect as the -s option.
The options for make are listed below:
-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 com-
mands.
-k Abandon work on the current entry if it
fails, but continue on other branches that
do not depend on that entry.
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make(1) USER COMMANDS make(1)
-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 defini-
tions and target descriptions.
-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 com-
mands.
Creating the makefile
The makefile invoked with the -f option 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:
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make(1) USER COMMANDS make(1)
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 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 below). 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 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.
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 and -p) 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 invo-
cations of commands. Thus, MAKEFLAGS always contains the
current input options. This feature proves very useful for
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make(1) USER COMMANDS make(1)
``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 charac-
ter 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 optional
:subst1=subst2 is a substitute sequence. If it is speci-
fied, 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 below.
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'' depen-
dent 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 $*.c
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make(1) USER COMMANDS make(1)
or:
.c.o:
cc -c -O $<
$? The $? macro is evaluated when explicit rules from the
makefile are evaluated. It is the list of prere-
quisites 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 gen-
erated. 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, etc. If no update
commands for such a file appear in 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 fol-
lowing 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
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make(1) USER COMMANDS make(1)
any file reference into an SCCS file reference.
A rule with only one suffix (for example, .c:) is the defin-
ition of how to build x from x.c. In effect, the other suf-
fix 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; .SUF-
FIXES: 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), respec-
tively. 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
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make(1) USER COMMANDS make(1)
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. An
unfortunate by-product of 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) $@ $*.o
rm -f $*.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 con-
struction 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 substi-
tution 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 con-
struct becomes very cumbersome if the archive library con-
tains a mix of assembly programs and C programs.
FILES
[Mm]akefile and s.[Mm]akefile
/usr/bin/sh
SEE ALSO
cc(1), lex(1), yacc(1), printf(3S), sccsfile(4).
cd(1), sh(1) in the User's Reference Manual.
See the ``make'' chapter in the Programmer's Guide: ANSI C
and Programming Support Tools.
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make(1) USER COMMANDS make(1)
NOTES
Some commands return non-zero status inappropriately; use -i
or the - command line prefix to overcome the difficulty.
Filenames with the characters = : @ 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.
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