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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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MAKE(1P) POSIX Programmer's Manual MAKE(1P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
make — maintain, update, and regenerate groups of programs
(DEVELOPMENT)
make [-einpqrst] [-f makefile]... [-k|-S] [macro=value...]
[target_name...]
The make utility shall update files that are derived from other
files. A typical case is one where object files are derived from
the corresponding source files. The make utility examines time
relationships and shall update those derived files (called
targets) that have modified times earlier than the modified times
of the files (called prerequisites) from which they are derived.
A description file (makefile) contains a description of the
relationships between files, and the commands that need to be
executed to update the targets to reflect changes in their
prerequisites. Each specification, or rule, shall consist of a
target, optional prerequisites, and optional commands to be
executed when a prerequisite is newer than the target. There are
two types of rule:
1. Inference rules, which have one target name with at least one
<period> ('.') and no <slash> ('/')
2. Target rules, which can have more than one target name
In addition, make shall have a collection of built-in macros and
inference rules that infer prerequisite relationships to simplify
maintenance of programs.
To receive exactly the behavior described in this section, the
user shall ensure that a portable makefile shall:
* Include the special target .POSIX
* Omit any special target reserved for implementations (a
leading period followed by uppercase letters) that has not
been specified by this section
The behavior of make is unspecified if either or both of these
conditions are not met.
The make utility shall conform to the Base Definitions volume of
POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines, except for
Guideline 9.
The following options shall be supported:
-e Cause environment variables, including those with null
values, to override macro assignments within makefiles.
-f makefile
Specify a different makefile. The argument makefile is
a pathname of a description file, which is also
referred to as the makefile. A pathname of '-' shall
denote the standard input. There can be multiple
instances of this option, and they shall be processed
in the order specified. The effect of specifying the
same option-argument more than once is unspecified.
-i Ignore error codes returned by invoked commands. This
mode is the same as if the special target .IGNORE were
specified without prerequisites.
-k Continue to update other targets that do not depend on
the current target if a non-ignored error occurs while
executing the commands to bring a target up-to-date.
-n Write commands that would be executed on standard
output, but do not execute them. However, lines with a
<plus-sign> ('+') prefix shall be executed. In this
mode, lines with an at-sign ('@') character prefix
shall be written to standard output.
-p Write to standard output the complete set of macro
definitions and target descriptions. The output format
is unspecified.
-q Return a zero exit value if the target file is up-to-
date; otherwise, return an exit value of 1. Targets
shall not be updated if this option is specified.
However, a makefile command line (associated with the
targets) with a <plus-sign> ('+') prefix shall be
executed.
-r Clear the suffix list and do not use the built-in
rules.
-S Terminate make if an error occurs while executing the
commands to bring a target up-to-date. This shall be
the default and the opposite of -k.
-s Do not write makefile command lines or touch messages
(see -t) to standard output before executing. This mode
shall be the same as if the special target .SILENT were
specified without prerequisites.
-t Update the modification time of each target as though a
touch target had been executed. Targets that have
prerequisites but no commands (see Target Rules), or
that are already up-to-date, shall not be touched in
this manner. Write messages to standard output for
each target file indicating the name of the file and
that it was touched. Normally, the makefile command
lines associated with each target are not executed.
However, a command line with a <plus-sign> ('+') prefix
shall be executed.
Any options specified in the MAKEFLAGS environment variable shall
be evaluated before any options specified on the make utility
command line. If the -k and -S options are both specified on the
make utility command line or by the MAKEFLAGS environment
variable, the last option specified shall take precedence. If
the -f or -p options appear in the MAKEFLAGS environment
variable, the result is undefined.
The following operands shall be supported:
target_name
Target names, as defined in the EXTENDED DESCRIPTION
section. If no target is specified, while make is
processing the makefiles, the first target that make
encounters that is not a special target or an inference
rule shall be used.
macro=value
Macro definitions, as defined in Macros.
If the target_name and macro=value operands are intermixed on the
make utility command line, the results are unspecified.
The standard input shall be used only if the makefile option-
argument is '-'. See the INPUT FILES section.
The input file, otherwise known as the makefile, is a text file
containing rules, macro definitions, include lines, and comments.
See the EXTENDED DESCRIPTION section.
The following environment variables shall affect the execution of
make:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base
Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of
internationalization variables used to determine the
values of locale categories.)
LC_ALL If set to a non-empty string value, override the values
of all the other internationalization variables.
LC_CTYPE Determine the locale for the interpretation of
sequences of bytes of text data as characters (for
example, single-byte as opposed to multi-byte
characters in arguments and input files).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
MAKEFLAGS
This variable shall be interpreted as a character
string representing a series of option characters to be
used as the default options. The implementation shall
accept both of the following formats (but need not
accept them when intermixed):
* The characters are option letters without the
leading <hyphen-minus> characters or <blank>
separation used on a make utility command line.
* The characters are formatted in a manner similar to
a portion of the make utility command line: options
are preceded by <hyphen-minus> characters and
<blank>-separated as described in the Base
Definitions volume of POSIX.1‐2017, Section 12.2,
Utility Syntax Guidelines. The macro=value macro
definition operands can also be included. The
difference between the contents of MAKEFLAGS and
the make utility command line is that the contents
of the variable shall not be subjected to the word
expansions (see Section 2.6, Word Expansions)
associated with parsing the command line values.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
PROJECTDIR
Provide a directory to be used to search for SCCS files
not found in the current directory. In all of the
following cases, the search for SCCS files is made in
the directory SCCS in the identified directory. If the
value of PROJECTDIR begins with a <slash>, it shall be
considered an absolute pathname; otherwise, the value
of PROJECTDIR is treated as a user name and that user's
initial working directory shall be examined for a
subdirectory src or source. If such a directory is
found, it shall be used. Otherwise, the value is used
as a relative pathname.
If PROJECTDIR is not set or has a null value, the
search for SCCS files shall be made in the directory
SCCS in the current directory.
The setting of PROJECTDIR affects all files listed in
the remainder of this utility description for files
with a component named SCCS.
The value of the SHELL environment variable shall not be used as
a macro and shall not be modified by defining the SHELL macro in
a makefile or on the command line. All other environment
variables, including those with null values, shall be used as
macros, as defined in Macros.
If not already ignored, make shall trap SIGHUP, SIGTERM, SIGINT,
and SIGQUIT and remove the current target unless the target is a
directory or the target is a prerequisite of the special target
.PRECIOUS or unless one of the -n, -p, or -q options was
specified. Any targets removed in this manner shall be reported
in diagnostic messages of unspecified format, written to standard
error. After this cleanup process, if any, make shall take the
standard action for all other signals.
The make utility shall write all commands to be executed to
standard output unless the -s option was specified, the command
is prefixed with an at-sign, or the special target .SILENT has
either the current target as a prerequisite or has no
prerequisites. If make is invoked without any work needing to be
done, it shall write a message to standard output indicating that
no action was taken. If the -t option is present and a file is
touched, make shall write to standard output a message of
unspecified format indicating that the file was touched,
including the filename of the file.
The standard error shall be used only for diagnostic messages.
Files can be created when the -t option is present. Additional
files can also be created by the utilities invoked by make.
The make utility attempts to perform the actions required to
ensure that the specified targets are up-to-date. A target shall
be considered up-to-date if it exists and is newer than all of
its dependencies, or if it has already been made up-to-date by
the current invocation of make (regardless of the target's
existence or age). A target may also be considered up-to-date if
it exists, is the same age as one or more of its prerequisites,
and is newer than the remaining prerequisites (if any). The make
utility shall treat all prerequisites as targets themselves and
recursively ensure that they are up-to-date, processing them in
the order in which they appear in the rule. The make utility
shall use the modification times of files to determine whether
the corresponding targets are out-of-date.
To ensure that a target is up-to-date, make shall ensure that all
of the prerequisites of a target are up-to-date, then check to
see if the target itself is up-to-date. If the target is not up-
to-date, the target shall be made up-to-date by executing the
rule's commands (if any). If the target does not exist after the
target has been successfully made up-to-date, the target shall be
treated as being newer than any target for which it is a
prerequisite.
If a target exists and there is neither a target rule nor an
inference rule for the target, the target shall be considered up-
to-date. It shall be an error if make attempts to ensure that a
target is up-to-date but the target does not exist and there is
neither a target rule nor an inference rule for the target.
Makefile Syntax
A makefile can contain rules, macro definitions (see Macros),
include lines, and comments. There are two kinds of rules:
inference rules and target rules. The make utility shall contain
a set of built-in inference rules. If the -r option is present,
the built-in rules shall not be used and the suffix list shall be
cleared. Additional rules of both types can be specified in a
makefile. If a rule is defined more than once, the value of the
rule shall be that of the last one specified. Macros can also be
defined more than once, and the value of the macro is specified
in Macros. There are three kinds of comments: blank lines, empty
lines, and a <number-sign> ('#') and all following characters up
to the first unescaped <newline> character. Blank lines, empty
lines, and lines with <number-sign> ('#') as the first character
on the line are also known as comment lines.
By default, the following files shall be tried in sequence:
./makefile and ./Makefile. If neither ./makefile or ./Makefile
are found, other implementation-defined files may also be tried.
On XSI-conformant systems, the additional files ./s.makefile,
SCCS/s.makefile, ./s.Makefile, and SCCS/s.Makefile shall also be
tried.
The -f option shall direct make to ignore any of these default
files and use the specified argument as a makefile instead. If
the '-' argument is specified, standard input shall be used.
The term makefile is used to refer to any rules provided by the
user, whether in ./makefile or its variants, or specified by the
-f option.
The rules in makefiles shall consist of the following types of
lines: target rules, including special targets (see Target
Rules), inference rules (see Inference Rules), macro definitions
(see Macros), and comments.
Target and Inference Rules may contain command lines. Command
lines can have a prefix that shall be removed before execution
(see Makefile Execution).
When an escaped <newline> (one preceded by a <backslash>) is
found anywhere in the makefile except in a command line, an
include line, or a line immediately preceding an include line, it
shall be replaced, along with any leading white space on the
following line, with a single <space>. When an escaped <newline>
is found in a command line in a makefile, the command line shall
contain the <backslash>, the <newline>, and the next line, except
that the first character of the next line shall not be included
if it is a <tab>. When an escaped <newline> is found in an
include line or in a line immediately preceding an include line,
the behavior is unspecified.
Include Lines
If the word include appears at the beginning of a line and is
followed by one or more <blank> characters, the string formed by
the remainder of the line shall be processed as follows to
produce a pathname:
* The trailing <newline>, any <blank> characters immediately
preceding a comment, and any comment shall be discarded. If
the resulting string contains any double-quote characters
('"') the behavior is unspecified.
* The resulting string shall be processed for macro expansion
(see Macros).
* Any <blank> characters that appear after the first
non-<blank> shall be used as separators to divide the macro-
expanded string into fields. It is unspecified whether any
other white-space characters are also used as separators. It
is unspecified whether pathname expansion (see Section 2.13,
Pattern Matching Notation) is also performed.
* If the processing of separators and optional pathname
expansion results in either zero or two or more non-empty
fields, the behavior is unspecified. If it results in one
non-empty field, that field is taken as the pathname.
If the pathname does not begin with a '/' it shall be treated as
relative to the current working directory of the process, not
relative to the directory containing the makefile. If the file
does not exist in this location, it is unspecified whether
additional directories are searched.
The contents of the file specified by the pathname shall be read
and processed as if they appeared in the makefile in place of the
include line. If the file ends with an escaped <newline> the
behavior is unspecified.
The file may itself contain further include lines.
Implementations shall support nesting of include files up to a
depth of at least 16.
Makefile Execution
Makefile command lines shall be processed one at a time.
Makefile command lines can have one or more of the following
prefixes: a <hyphen-minus> ('-'), an at-sign ('@'), or a <plus-
sign> ('+'). These shall modify the way in which make processes
the command.
- If the command prefix contains a <hyphen-minus>, or the -i
option is present, or the special target .IGNORE has either
the current target as a prerequisite or has no
prerequisites, any error found while executing the command
shall be ignored.
@ If the command prefix contains an at-sign and the make
utility command line -n option is not specified, or the -s
option is present, or the special target .SILENT has either
the current target as a prerequisite or has no
prerequisites, the command shall not be written to standard
output before it is executed.
+ If the command prefix contains a <plus-sign>, this
indicates a makefile command line that shall be executed
even if -n, -q, or -t is specified.
An execution line is built from the command line by removing any
prefix characters. Except as described under the at-sign prefix,
the execution line shall be written to the standard output,
optionally preceded by a <tab>. The execution line shall then be
executed by a shell as if it were passed as the argument to the
system() interface, except that if errors are not being ignored
then the shell -e option shall also be in effect. If errors are
being ignored for the command (as a result of the -i option, a
'-' command prefix, or a .IGNORE special target), the shell -e
option shall not be in effect. The environment for the command
being executed shall contain all of the variables in the
environment of make.
By default, when make receives a non-zero status from the
execution of a command, it shall terminate with an error message
to standard error.
Target Rules
Target rules are formatted as follows:
target [target...]: [prerequisite...][;command]
[<tab>command
<tab>command
...]
line that does not begin with <tab>
Target entries are specified by a <blank>-separated, non-null
list of targets, then a <colon>, then a <blank>-separated,
possibly empty list of prerequisites. Text following a
<semicolon>, if any, and all following lines that begin with a
<tab>, are makefile command lines to be executed to update the
target. The first non-empty line that does not begin with a <tab>
or '#' shall begin a new entry. Any comment line may begin a new
entry.
Applications shall select target names from the set of characters
consisting solely of periods, underscores, digits, and
alphabetics from the portable character set (see the Base
Definitions volume of POSIX.1‐2017, Section 6.1, Portable
Character Set). Implementations may allow other characters in
target names as extensions. The interpretation of targets
containing the characters '%' and '"' is implementation-defined.
A target that has prerequisites, but does not have any commands,
can be used to add to the prerequisite list for that target. Only
one target rule for any given target can contain commands.
Lines that begin with one of the following are called special
targets and control the operation of make:
.DEFAULT If the makefile uses this special target, the
application shall ensure that it is specified with
commands, but without prerequisites. The commands shall
be used by make if there are no other rules available
to build a target.
.IGNORE Prerequisites of this special target are targets
themselves; this shall cause errors from commands
associated with them to be ignored in the same manner
as specified by the -i option. Subsequent occurrences
of .IGNORE shall add to the list of targets ignoring
command errors. If no prerequisites are specified, make
shall behave as if the -i option had been specified and
errors from all commands associated with all targets
shall be ignored.
.POSIX The application shall ensure that this special target
is specified without prerequisites or commands. If it
appears as the first non-comment line in the makefile,
make shall process the makefile as specified by this
section; otherwise, the behavior of make is
unspecified.
.PRECIOUS Prerequisites of this special target shall not be
removed if make receives one of the asynchronous events
explicitly described in the ASYNCHRONOUS EVENTS
section. Subsequent occurrences of .PRECIOUS shall add
to the list of precious files. If no prerequisites are
specified, all targets in the makefile shall be treated
as if specified with .PRECIOUS.
.SCCS_GET The application shall ensure that this special target
is specified without prerequisites. If this special
target is included in a makefile, the commands
specified with this target shall replace the default
commands associated with this special target (see
Default Rules). The commands specified with this
target are used to get all SCCS files that are not
found in the current directory.
When source files are named in a dependency list, make
shall treat them just like any other target. Because
the source file is presumed to be present in the
directory, there is no need to add an entry for it to
the makefile. When a target has no dependencies, but is
present in the directory, make shall assume that that
file is up-to-date. If, however, an SCCS file named
SCCS/s.source_file is found for a target source_file,
make compares the timestamp of the target file with
that of the SCCS/s.source_file to ensure the target is
up-to-date. If the target is missing, or if the SCCS
file is newer, make shall automatically issue the
commands specified for the .SCCS_GET special target to
retrieve the most recent version. However, if the
target is writable by anyone, make shall not retrieve a
new version.
.SILENT Prerequisites of this special target are targets
themselves; this shall cause commands associated with
them not to be written to the standard output before
they are executed. Subsequent occurrences of .SILENT
shall add to the list of targets with silent commands.
If no prerequisites are specified, make shall behave as
if the -s option had been specified and no commands or
touch messages associated with any target shall be
written to standard output.
.SUFFIXES Prerequisites of .SUFFIXES shall be appended to the
list of known suffixes and are used in conjunction with
the inference rules (see Inference Rules). If
.SUFFIXES does not have any prerequisites, the list of
known suffixes shall be cleared.
The special targets .IGNORE, .POSIX, .PRECIOUS, .SILENT, and
.SUFFIXES shall be specified without commands.
Targets with names consisting of a leading <period> followed by
the uppercase letters "POSIX" and then any other characters are
reserved for future standardization. Targets with names
consisting of a leading <period> followed by one or more
uppercase letters are reserved for implementation extensions.
Macros
Macro definitions are in the form:
string1 = [string2]
The macro named string1 is defined as having the value of
string2, where string2 is defined as all characters, if any,
after the <equals-sign>, up to a comment character ('#') or an
unescaped <newline>. Any <blank> characters immediately before
or after the <equals-sign> shall be ignored.
Applications shall select macro names from the set of characters
consisting solely of periods, underscores, digits, and
alphabetics from the portable character set (see the Base
Definitions volume of POSIX.1‐2017, Section 6.1, Portable
Character Set). A macro name shall not contain an <equals-sign>.
Implementations may allow other characters in macro names as
extensions.
Macros can appear anywhere in the makefile. Macro expansions
using the forms $(string1) or ${string1} shall be replaced by
string2, as follows:
* Macros in target lines shall be evaluated when the target
line is read.
* Macros in makefile command lines shall be evaluated when the
command is executed.
* Macros in the string before the <equals-sign> in a macro
definition shall be evaluated when the macro assignment is
made.
* Macros after the <equals-sign> in a macro definition shall
not be evaluated until the defined macro is used in a rule or
command, or before the <equals-sign> in a macro definition.
The parentheses or braces are optional if string1 is a single
character. The macro $$ shall be replaced by the single character
'$'. If string1 in a macro expansion contains a macro expansion,
the results are unspecified.
Macro expansions using the forms $(string1[:subst1=[subst2]]) or
${string1[:subst1=[subst2]]} can be used to replace all
occurrences of subst1 with subst2 when the macro substitution is
performed. The subst1 to be replaced shall be recognized when it
is a suffix at the end of a word in string1 (where a word, in
this context, is defined to be a string delimited by the
beginning of the line, a <blank>, or a <newline>). If string1 in
a macro expansion contains a macro expansion, the results are
unspecified. If a <percent-sign> character appears as part of
subst1 or subst2 after any macros have been recursively expanded,
the results are unspecified.
Macro expansions in string1 of macro definition lines shall be
evaluated when read. Macro expansions in string2 of macro
definition lines shall be performed when the macro identified by
string1 is expanded in a rule or command.
Macro definitions shall be taken from the following sources, in
the following logical order, before the makefile(s) are read.
1. Macros specified on the make utility command line, in the
order specified on the command line. It is unspecified
whether the internal macros defined in Internal Macros are
accepted from this source.
2. Macros defined by the MAKEFLAGS environment variable, in the
order specified in the environment variable. It is
unspecified whether the internal macros defined in Internal
Macros are accepted from this source.
3. The contents of the environment, excluding the MAKEFLAGS and
SHELL variables and including the variables with null values.
4. Macros defined in the inference rules built into make.
Macro definitions from these sources shall not override macro
definitions from a lower-numbered source. Macro definitions from
a single source (for example, the make utility command line, the
MAKEFLAGS environment variable, or the other environment
variables) shall override previous macro definitions from the
same source.
Macros defined in the makefile(s) shall override macro
definitions that occur before them in the makefile(s) and macro
definitions from source 4. If the -e option is not specified,
macros defined in the makefile(s) shall override macro
definitions from source 3. Macros defined in the makefile(s)
shall not override macro definitions from source 1 or source 2.
Before the makefile(s) are read, all of the make utility command
line options (except -f and -p) and make utility command line
macro definitions (except any for the MAKEFLAGS macro), not
already included in the MAKEFLAGS macro, shall be added to the
MAKEFLAGS macro, quoted in an implementation-defined manner such
that when MAKEFLAGS is read by another instance of the make
command, the original macro's value is recovered. Other
implementation-defined options and macros may also be added to
the MAKEFLAGS macro. If this modifies the value of the MAKEFLAGS
macro, or, if the MAKEFLAGS macro is modified at any subsequent
time, the MAKEFLAGS environment variable shall be modified to
match the new value of the MAKEFLAGS macro. The result of setting
MAKEFLAGS in the Makefile is unspecified.
Before the makefile(s) are read, all of the make utility command
line macro definitions (except the MAKEFLAGS macro or the SHELL
macro) shall be added to the environment of make. Other
implementation-defined variables may also be added to the
environment of make. Macros defined by the MAKEFLAGS environment
variable and macros defined in the makefile(s) shall not be added
to the environment of make if they are not already in its
environment. With the exception of SHELL (see below), it is
unspecified whether macros defined in these ways update the value
of an environment variable that already exists in the environment
of make.
The SHELL macro shall be treated specially. It shall be provided
by make and set to the pathname of the shell command language
interpreter (see sh(1p)). The SHELL environment variable shall
not affect the value of the SHELL macro. If SHELL is defined in
the makefile or is specified on the command line, it shall
replace the original value of the SHELL macro, but shall not
affect the SHELL environment variable. Other effects of defining
SHELL in the makefile or on the command line are implementation-
defined.
Inference Rules
Inference rules are formatted as follows:
target:
<tab>command
[<tab>command]
...
line that does not begin with <tab> or #
The application shall ensure that the target portion is a valid
target name (see Target Rules) of the form .s2 or .s1.s2 (where
.s1 and .s2 are suffixes that have been given as prerequisites of
the .SUFFIXES special target and s1 and s2 do not contain any
<slash> or <period> characters.) If there is only one <period> in
the target, it is a single-suffix inference rule. Targets with
two periods are double-suffix inference rules. Inference rules
can have only one target before the <colon>.
The application shall ensure that the makefile does not specify
prerequisites for inference rules; no characters other than white
space shall follow the <colon> in the first line, except when
creating the empty rule, described below. Prerequisites are
inferred, as described below.
Inference rules can be redefined. A target that matches an
existing inference rule shall overwrite the old inference rule.
An empty rule can be created with a command consisting of simply
a <semicolon> (that is, the rule still exists and is found during
inference rule search, but since it is empty, execution has no
effect). The empty rule can also be formatted as follows:
rule: ;
where zero or more <blank> characters separate the <colon> and
<semicolon>.
The make utility uses the suffixes of targets and their
prerequisites to infer how a target can be made up-to-date. A
list of inference rules defines the commands to be executed. By
default, make contains a built-in set of inference rules.
Additional rules can be specified in the makefile.
The special target .SUFFIXES contains as its prerequisites a list
of suffixes that shall be used by the inference rules. The order
in which the suffixes are specified defines the order in which
the inference rules for the suffixes are used. New suffixes shall
be appended to the current list by specifying a .SUFFIXES special
target in the makefile. A .SUFFIXES target with no prerequisites
shall clear the list of suffixes. An empty .SUFFIXES target
followed by a new .SUFFIXES list is required to change the order
of the suffixes.
Normally, the user would provide an inference rule for each
suffix. The inference rule to update a target with a suffix .s1
from a prerequisite with a suffix .s2 is specified as a target
.s2.s1. The internal macros provide the means to specify general
inference rules (see Internal Macros).
When no target rule is found to update a target, the inference
rules shall be checked. The suffix of the target (.s1) to be
built is compared to the list of suffixes specified by the
.SUFFIXES special targets. If the .s1 suffix is found in
.SUFFIXES, the inference rules shall be searched in the order
defined for the first .s2.s1 rule whose prerequisite file ($*.s2)
exists. If the target is out-of-date with respect to this
prerequisite, the commands for that inference rule shall be
executed.
If the target to be built does not contain a suffix and there is
no rule for the target, the single suffix inference rules shall
be checked. The single-suffix inference rules define how to build
a target if a file is found with a name that matches the target
name with one of the single suffixes appended. A rule with one
suffix .s2 is the definition of how to build target from
target.s2. The other suffix (.s1) is treated as null.
A <tilde> ('~') in the above rules refers to an SCCS file in the
current directory. Thus, the rule .c~.o would transform an SCCS
C-language source file into an object file (.o). Because the s.
of the SCCS files is a prefix, it is incompatible with make's
suffix point of view. Hence, the '~' is a way of changing any
file reference into an SCCS file reference.
Libraries
If a target or prerequisite contains parentheses, it shall be
treated as a member of an archive library. For the lib(member.o)
expression lib refers to the name of the archive library and
member.o to the member name. The application shall ensure that
the member is an object file with the .o suffix. The modification
time of the expression is the modification time for the member as
kept in the archive library; see ar(1p). The .a suffix shall
refer to an archive library. The .s2.a rule shall be used to
update a member in the library from a file with a suffix .s2.
Internal Macros
The make utility shall maintain five internal macros that can be
used in target and inference rules. In order to clearly define
the meaning of these macros, some clarification of the terms
target rule, inference rule, target, and prerequisite is
necessary.
Target rules are specified by the user in a makefile for a
particular target. Inference rules are user-specified or make-
specified rules for a particular class of target name. Explicit
prerequisites are those prerequisites specified in a makefile on
target lines. Implicit prerequisites are those prerequisites
that are generated when inference rules are used. Inference rules
are applied to implicit prerequisites or to explicit
prerequisites that do not have target rules defined for them in
the makefile. Target rules are applied to targets specified in
the makefile.
Before any target in the makefile is updated, each of its
prerequisites (both explicit and implicit) shall be updated. This
shall be accomplished by recursively processing each
prerequisite. Upon recursion, each prerequisite shall become a
target itself. Its prerequisites in turn shall be processed
recursively until a target is found that has no prerequisites, or
further recursion would require applying two inference rules one
immediately after the other, at which point the recursion shall
stop. As an extension, implementations may continue recursion
when two or more successive inference rules need to be applied;
however, if there are multiple different chains of such rules
that could be used to create the target, it is unspecified which
chain is used. The recursion shall then back up, updating each
target as it goes.
In the definitions that follow, the word target refers to one of:
* A target specified in the makefile
* An explicit prerequisite specified in the makefile that
becomes the target when make processes it during recursion
* An implicit prerequisite that becomes a target when make
processes it during recursion
In the definitions that follow, the word prerequisite refers to
one of the following:
* An explicit prerequisite specified in the makefile for a
particular target
* An implicit prerequisite generated as a result of locating an
appropriate inference rule and corresponding file that
matches the suffix of the target
The five internal macros are:
$@ The $@ shall evaluate to the full target name of the
current target, or the archive filename part of a library
archive target. It shall be evaluated for both target and
inference rules.
For example, in the .c.a inference rule, $@ represents
the out-of-date .a file to be built. Similarly, in a
makefile target rule to build lib.a from file.c, $@
represents the out-of-date lib.a.
$% The $% macro shall be evaluated only when the current
target is an archive library member of the form
libname(member.o). In these cases, $@ shall evaluate to
libname and $% shall evaluate to member.o. The $% macro
shall be evaluated for both target and inference rules.
For example, in a makefile target rule to build
lib.a(file.o), $% represents file.o, as opposed to $@,
which represents lib.a.
$? The $? macro shall evaluate to the list of prerequisites
that are newer than the current target. It shall be
evaluated for both target and inference rules.
For example, in a makefile target rule to build prog from
file1.o, file2.o, and file3.o, and where prog is not out-
of-date with respect to file1.o, but is out-of-date with
respect to file2.o and file3.o, $? represents file2.o and
file3.o.
$< In an inference rule, the $< macro shall evaluate to the
filename whose existence allowed the inference rule to be
chosen for the target. In the .DEFAULT rule, the $<
macro shall evaluate to the current target name. The
meaning of the $< macro shall be otherwise unspecified.
For example, in the .c.a inference rule, $< represents
the prerequisite .c file.
$* The $* macro shall evaluate to the current target name
with its suffix deleted. It shall be evaluated at least
for inference rules.
For example, in the .c.a inference rule, $*.o represents
the out-of-date .o file that corresponds to the
prerequisite .c file.
Each of the internal macros has an alternative form. When an
uppercase 'D' or 'F' is appended to any of the macros, the
meaning shall be changed to the directory part for 'D' and
filename part for 'F'. The directory part is the path prefix of
the file without a trailing <slash>; for the current directory,
the directory part is '.'. When the $? macro contains more than
one prerequisite filename, the $(?D) and $(?F) (or ${?D} and
${?F}) macros expand to a list of directory name parts and
filename parts respectively.
For the target lib(member.o) and the s2.a rule, the internal
macros shall be defined as:
$< member.s2
$* member
$@ lib
$? member.s2
$% member.o
Default Rules
The default rules for make shall achieve results that are the
same as if the following were used. Implementations that do not
support the C-Language Development Utilities option may omit CC,
CFLAGS, YACC, YFLAGS, LEX, LFLAGS, LDFLAGS, and the .c, .y, and
.l inference rules. Implementations that do not support FORTRAN
may omit FC, FFLAGS, and the .f inference rules. Implementations
may provide additional macros and rules.
SPECIAL TARGETS
.SCCS_GET: sccs $(SCCSFLAGS) get $(SCCSGETFLAGS) $@
.SUFFIXES: .o .c .y .l .a .sh .f .c~ .y~ .l~ .sh~ .f~
MACROS
MAKE=make
AR=ar
ARFLAGS=-rv
YACC=yacc
YFLAGS=
LEX=lex
LFLAGS=
LDFLAGS=
CC=c99
CFLAGS=-O 1
FC=fort77
FFLAGS=-O 1
GET=get
GFLAGS=
SCCSFLAGS=
SCCSGETFLAGS=-s
SINGLE SUFFIX RULES
.c:
$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $<
.f:
$(FC) $(FFLAGS) $(LDFLAGS) -o $@ $<
.sh:
cp $< $@
chmod a+x $@
.c~:
$(GET) $(GFLAGS) -p $< > $*.c
$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $*.c
.f~:
$(GET) $(GFLAGS) -p $< > $*.f
$(FC) $(FFLAGS) $(LDFLAGS) -o $@ $*.f
.sh~:
$(GET) $(GFLAGS) -p $< > $*.sh
cp $*.sh $@
chmod a+x $@
DOUBLE SUFFIX RULES
.c.o:
$(CC) $(CFLAGS) -c $<
.f.o:
$(FC) $(FFLAGS) -c $<
.y.o:
$(YACC) $(YFLAGS) $<
$(CC) $(CFLAGS) -c y.tab.c
rm -f y.tab.c
mv y.tab.o $@
.l.o:
$(LEX) $(LFLAGS) $<
$(CC) $(CFLAGS) -c lex.yy.c
rm -f lex.yy.c
mv lex.yy.o $@
.y.c:
$(YACC) $(YFLAGS) $<
mv y.tab.c $@
.l.c:
$(LEX) $(LFLAGS) $<
mv lex.yy.c $@
.c~.o:
$(GET) $(GFLAGS) -p $< > $*.c
$(CC) $(CFLAGS) -c $*.c
.f~.o:
$(GET) $(GFLAGS) -p $< > $*.f
$(FC) $(FFLAGS) -c $*.f
.y~.o:
$(GET) $(GFLAGS) -p $< > $*.y
$(YACC) $(YFLAGS) $*.y
$(CC) $(CFLAGS) -c y.tab.c
rm -f y.tab.c
mv y.tab.o $@
.l~.o:
$(GET) $(GFLAGS) -p $< > $*.l
$(LEX) $(LFLAGS) $*.l
$(CC) $(CFLAGS) -c lex.yy.c
rm -f lex.yy.c
mv lex.yy.o $@
.y~.c:
$(GET) $(GFLAGS) -p $< > $*.y
$(YACC) $(YFLAGS) $*.y
mv y.tab.c $@
.l~.c:
$(GET) $(GFLAGS) -p $< > $*.l
$(LEX) $(LFLAGS) $*.l
mv lex.yy.c $@
.c.a:
$(CC) -c $(CFLAGS) $<
$(AR) $(ARFLAGS) $@ $*.o
rm -f $*.o
.f.a:
$(FC) -c $(FFLAGS) $<
$(AR) $(ARFLAGS) $@ $*.o
rm -f $*.o
When the -q option is specified, the make utility shall exit with
one of the following values:
0 Successful completion.
1 The target was not up-to-date.
>1 An error occurred.
When the -q option is not specified, the make utility shall exit
with one of the following values:
0 Successful completion.
>0 An error occurred.
Default.
The following sections are informative.
If there is a source file (such as ./source.c) and there are two
SCCS files corresponding to it (./s.source.c and
./SCCS/s.source.c), on XSI-conformant systems make uses the SCCS
file in the current directory. However, users are advised to use
the underlying SCCS utilities (admin, delta, get, and so on) or
the sccs utility for all source files in a given directory. If
both forms are used for a given source file, future developers
are very likely to be confused.
It is incumbent upon portable makefiles to specify the .POSIX
special target in order to guarantee that they are not affected
by local extensions.
The -k and -S options are both present so that the relationship
between the command line, the MAKEFLAGS variable, and the
makefile can be controlled precisely. If the k flag is passed in
MAKEFLAGS and a command is of the form:
$(MAKE) -S foo
then the default behavior is restored for the child make.
When the -n option is specified, it is always added to MAKEFLAGS.
This allows a recursive make -n target to be used to see all of
the action that would be taken to update target.
Because of widespread historical practice, interpreting a
<number-sign> ('#') inside a variable as the start of a comment
has the unfortunate side-effect of making it impossible to place
a <number-sign> in a variable, thus forbidding something like:
CFLAGS = "-D COMMENT_CHAR='#'"
Many historical make utilities stop chaining together inference
rules when an intermediate target is nonexistent. For example, it
might be possible for a make to determine that both .y.c and .c.o
could be used to convert a .y to a .o. Instead, in this case,
make requires the use of a .y.o rule.
The best way to provide portable makefiles is to include all of
the rules needed in the makefile itself. The rules provided use
only features provided by other parts of this volume of
POSIX.1‐2017. The default rules include rules for optional
commands in this volume of POSIX.1‐2017. Only rules pertaining to
commands that are provided are needed in an implementation's
default set.
Macros used within other macros are evaluated when the new macro
is used rather than when the new macro is defined. Therefore:
MACRO = value1
NEW = $(MACRO)
MACRO = value2
target:
echo $(NEW)
would produce value2 and not value1 since NEW was not expanded
until it was needed in the echo command line.
Some historical applications have been known to intermix
target_name and macro=name operands on the command line,
expecting that all of the macros are processed before any of the
targets are dealt with. Conforming applications do not do this,
although some backwards-compatibility support may be included in
some implementations.
The following characters in filenames may give trouble: '=', ':',
'`', single-quote, and '@'. In include filenames, pattern
matching characters and '"' should also be avoided, as they may
be treated as special by some implementations.
For inference rules, the description of $< and $? seem similar.
However, an example shows the minor difference. In a makefile
containing:
foo.o: foo.h
if foo.h is newer than foo.o, yet foo.c is older than foo.o, the
built-in rule to make foo.o from foo.c is used, with $< equal to
foo.c and $? equal to foo.h. If foo.c is also newer than foo.o,
$< is equal to foo.c and $? is equal to foo.h foo.c.
As a consequence of the general rules for target updating, a
useful special case is that if a target has no prerequisites and
no commands, and the target of the rule is a nonexistent file,
then make acts as if this target has been updated whenever its
rule is run.
Note: This implies that all targets depending on this one will
always have their commands run.
Shell command sequences like make; cp original copy; make may
have problems on filesystems where the timestamp resolution is
the minimum (1 second) required by the standard and where make
considers identical timestamps to be up-to-date. Conversely,
rules like copy: original; cp -p original copy will result in
redundant work on make implementations that consider identical
timestamps to be out-of-date.
This standard does not specify precedence between macro
definition and include directives. Thus, the behavior of:
include =foo.mk
is unspecified. To define a variable named include, either the
white space before the <equal-sign> should be removed, or another
macro should be used, as in:
INCLUDE_NAME = include
$(INCLUDE_NAME) =foo.mk
On the other hand, if the intent is to include a file which
starts with an <equal-sign>, either the filename should be
changed to ./=foo.mk, or the makefile should be written as:
INCLUDE_FILE = =foo.mk
include $(INCLUDE_FILE)
1. The following command:
make
makes the first target found in the makefile.
2. The following command:
make junk
makes the target junk.
3. 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:
.POSIX:
pgm: a.o b.o
c99 a.o b.o -o pgm
a.o: incl.h a.c
c99 -c a.c
b.o: incl.h b.c
c99 -c b.c
4. An example for making optimized .o files from .c files is:
.c.o:
c99 -c -O 1 $*.c
or:
.c.o:
c99 -c -O 1 $<
5. The most common use of the archive interface follows. Here,
it is assumed that the source files are all C-language
source:
lib: lib(file1.o) lib(file2.o) lib(file3.o)
@echo lib is now up-to-date
The .c.a rule is used to make file1.o, file2.o, and file3.o
and insert them into lib.
The treatment of escaped <newline> characters throughout the
makefile is historical practice. For example, the inference
rule:
.c.o\
:
works, and the macro:
f= bar baz\
biz
a:
echo ==$f==
echoes "==bar baz biz==".
If $? were:
/usr/include/stdio.h /usr/include/unistd.h foo.h
then $(?D) would be:
/usr/include /usr/include .
and $(?F) would be:
stdio.h unistd.h foo.h
6. The contents of the built-in rules can be viewed by running:
make -p -f /dev/null 2>/dev/null
The make utility described in this volume of POSIX.1‐2017 is
intended to provide the means for changing portable source code
into executables that can be run on an POSIX.1‐2008-conforming
system. It reflects the most common features present in System V
and BSD makes.
Historically, the make utility has been an especially fertile
ground for vendor and research organization-specific syntax
modifications and extensions. Examples include:
* Syntax supporting parallel execution (such as from various
multi-processor vendors, GNU, and others)
* Additional ``operators'' separating targets and their
prerequisites (System V, BSD, and others)
* Specifying that command lines containing the strings
"${MAKE}" and "$(MAKE)" are executed when the -n option is
specified (GNU and System V)
* Modifications of the meaning of internal macros when
referencing libraries (BSD and others)
* Using a single instance of the shell for all of the command
lines of the target (BSD and others)
* Allowing <space> characters as well as <tab> characters to
delimit command lines (BSD)
* Adding C preprocessor-style ``include'' and ``ifdef''
constructs (System V, GNU, BSD, and others)
* Remote execution of command lines (Sprite and others)
* Specifying additional special targets (BSD, System V, and
most others)
* Specifying an alternate shell to use to process commands.
Additionally, many vendors and research organizations have
rethought the basic concepts of make, creating vastly extended,
as well as completely new, syntaxes. Each of these versions of
make fulfills the needs of a different community of users; it is
unreasonable for this volume of POSIX.1‐2017 to require behavior
that would be incompatible (and probably inferior) to historical
practice for such a community.
In similar circumstances, when the industry has enough
sufficiently incompatible formats as to make them irreconcilable,
this volume of POSIX.1‐2017 has followed one or both of two
courses of action. Commands have been renamed (cksum, echo, and
pax) and/or command line options have been provided to select the
desired behavior (grep, od, and pax).
Because the syntax specified for the make utility is, by and
large, a subset of the syntaxes accepted by almost all versions
of make, it was decided that it would be counter-productive to
change the name. And since the makefile itself is a basic unit
of portability, it would not be completely effective to reserve a
new option letter, such as make -P, to achieve the portable
behavior. Therefore, the special target .POSIX was added to the
makefile, allowing users to specify ``standard'' behavior. This
special target does not preclude extensions in the make utility,
nor does it preclude such extensions being used by the makefile
specifying the target; it does, however, preclude any extensions
from being applied that could alter the behavior of previously
valid syntax; such extensions must be controlled via command line
options or new special targets. It is incumbent upon portable
makefiles to specify the .POSIX special target in order to
guarantee that they are not affected by local extensions.
The portable version of make described in this reference page is
not intended to be the state-of-the-art software generation tool
and, as such, some newer and more leading-edge features have not
been included. An attempt has been made to describe the portable
makefile in a manner that does not preclude such extensions as
long as they do not disturb the portable behavior described here.
When the -n option is specified, it is always added to MAKEFLAGS.
This allows a recursive make -n target to be used to see all of
the action that would be taken to update target.
The definition of MAKEFLAGS allows both the System V letter
string and the BSD command line formats. The two formats are
sufficiently different to allow implementations to support both
without ambiguity.
Early proposals stated that an ``unquoted'' <number-sign> was
treated as the start of a comment. The make utility does not pay
any attention to quotes. A <number-sign> starts a comment
regardless of its surroundings.
The text about ``other implementation-defined pathnames may also
be tried'' in addition to ./makefile and ./Makefile is to allow
such extensions as SCCS/s.Makefile and other variations. It was
made an implementation-defined requirement (as opposed to
unspecified behavior) to highlight surprising implementations
that might select something unexpected like /etc/Makefile. XSI-
conformant systems also try ./s.makefile, SCCS/s.makefile,
./s.Makefile, and SCCS/s.Makefile.
Early proposals contained the macro NPROC as a means of
specifying that make should use n processes to do the work
required. While this feature is a valuable extension for many
systems, it is not common usage and could require other non-
trivial extensions to makefile syntax. This extension is not
required by this volume of POSIX.1‐2017, but could be provided as
a compatible extension. The macro PARALLEL is used by some
historical systems with essentially the same meaning (but without
using a name that is a common system limit value). It is
suggested that implementors recognize the existing use of NPROC
and/or PARALLEL as extensions to make.
The default rules are based on System V. The default CC= value is
c99 instead of cc because this volume of POSIX.1‐2017 does not
standardize the utility named cc. Thus, every conforming
application would be required to define CC=c99 to expect to run.
There is no advantage conferred by the hope that the makefile
might hit the ``preferred'' compiler because this cannot be
guaranteed to work. Also, since the portable makescript can only
use the c99 options, no advantage is conferred in terms of what
the script can do. It is a quality-of-implementation issue as to
whether c99 is as valuable as cc.
The -d option to make is frequently used to produce debugging
information, but is too implementation-defined to add to this
volume of POSIX.1‐2017.
The -p option is not passed in MAKEFLAGS on most historical
implementations and to change this would cause many
implementations to break without sufficiently increased
portability.
Commands that begin with a <plus-sign> ('+') are executed even if
the -n option is present. Based on the GNU version of make, the
behavior of -n when the <plus-sign> prefix is encountered has
been extended to apply to -q and -t as well. However, the System
V convention of forcing command execution with -n when the
command line of a target contains either of the strings "$(MAKE)"
or "${MAKE}" has not been adopted. This functionality appeared in
early proposals, but the danger of this approach was pointed out
with the following example of a portion of a makefile:
subdir:
cd subdir; rm all_the_files; $(MAKE)
The loss of the System V behavior in this case is well-balanced
by the safety afforded to other makefiles that were not aware of
this situation. In any event, the command line <plus-sign> prefix
can provide the desired functionality.
The double <colon> in the target rule format is supported in BSD
systems to allow more than one target line containing the same
target name to have commands associated with it. Since this is
not functionality described in the SVID or XPG3 it has been
allowed as an extension, but not mandated.
The default rules are provided with text specifying that the
built-in rules shall be the same as if the listed set were used.
The intent is that implementations should be able to use the
rules without change, but will be allowed to alter them in ways
that do not affect the primary behavior.
One point of discussion was whether to drop the default rules
list from this volume of POSIX.1‐2017. They provide convenience,
but do not enhance portability of applications. The prime benefit
is in portability of users who wish to type make command and have
the command build from a command.c file.
The historical MAKESHELL feature, and related features provided
by other make implementations, were omitted. In some
implementations it is used to let a user override the shell to be
used to run make commands. This was confusing; for a portable
make, the shell should be chosen by the makefile writer. Further,
a makefile writer cannot require an alternate shell to be used
and still consider the makefile portable. While it would be
possible to standardize a mechanism for specifying an alternate
shell, existing implementations do not agree on such a mechanism,
and makefile writers can already invoke an alternate shell by
specifying the shell name in the rule for a target; for example:
python -c "foo"
The make utilities in most historical implementations process the
prerequisites of a target in left-to-right order, and the
makefile format requires this. It supports the standard idiom
used in many makefiles that produce yacc programs; for example:
foo: y.tab.o lex.o main.o
$(CC) $(CFLAGS) -o $@ t.tab.o lex.o main.o
In this example, if make chose any arbitrary order, the lex.o
might not be made with the correct y.tab.h. Although there may
be better ways to express this relationship, it is widely used
historically. Implementations that desire to update prerequisites
in parallel should require an explicit extension to make or the
makefile format to accomplish it, as described previously.
The algorithm for determining a new entry for target rules is
partially unspecified. Some historical makes allow comment lines
(including blank and empty lines) within the collection of
commands marked by leading <tab> characters. A conforming
makefile must ensure that each command starts with a <tab>, but
implementations are free to ignore comments without triggering
the start of a new entry.
The ASYNCHRONOUS EVENTS section includes having SIGTERM and
SIGHUP, along with the more traditional SIGINT and SIGQUIT,
remove the current target unless directed not to do so. SIGTERM
and SIGHUP were added to parallel other utilities that have
historically cleaned up their work as a result of these signals.
When make receives any signal other than SIGQUIT, it is required
to resend itself the signal it received so that it exits with a
status that reflects the signal. The results from SIGQUIT are
partially unspecified because, on systems that create core files
upon receipt of SIGQUIT, the core from make would conflict with a
core file from the command that was running when the SIGQUIT
arrived. The main concern was to prevent damaged files from
appearing up-to-date when make is rerun.
The .PRECIOUS special target was extended to affect all targets
globally (by specifying no prerequisites). The .IGNORE and
.SILENT special targets were extended to allow prerequisites; it
was judged to be more useful in some cases to be able to turn off
errors or echoing for a list of targets than for the entire
makefile. These extensions to make in System V were made to match
historical practice from the BSD make.
Macros are not exported to the environment of commands to be run.
This was never the case in any historical make and would have
serious consequences. The environment is the same as the
environment to make except that MAKEFLAGS and macros defined on
the make command line are added, and except that macros defined
by the MAKEFLAGS environment variable and macros defined in the
makefile(s) may update the value of an existing environment
variable (other than SHELL).
Some implementations do not use system() for all command lines,
as required by the portable makefile format; as a performance
enhancement, they select lines without shell metacharacters for
direct execution by execve(). There is no requirement that
system() be used specifically, but merely that the same results
be achieved. The metacharacters typically used to bypass the
direct execve() execution have been any of:
= | ^ ( ) ; & < > * ? [ ] : $ ` ' " \ \n
The default in some advanced versions of make is to group all the
command lines for a target and execute them using a single shell
invocation; the System V method is to pass each line individually
to a separate shell. The single-shell method has the advantages
in performance and the lack of a requirement for many continued
lines. However, converting to this newer method has caused
portability problems with many historical makefiles, so the
behavior with the POSIX makefile is specified to be the same as
that of System V. It is suggested that the special target
.ONESHELL be used as an implementation extension to achieve the
single-shell grouping for a target or group of targets.
Novice users of make have had difficulty with the historical need
to start commands with a <tab>. Since it is often difficult to
discern differences between <tab> and <space> characters on
terminals or printed listings, confusing bugs can arise. In early
proposals, an attempt was made to correct this problem by
allowing leading <blank> characters instead of <tab> characters.
However, implementors reported many makefiles that failed in
subtle ways following this change, and it is difficult to
implement a make that unambiguously can differentiate between
macro and command lines. There is extensive historical practice
of allowing leading <space> characters before macro definitions.
Forcing macro lines into column 1 would be a significant
backwards-compatibility problem for some makefiles. Therefore,
historical practice was restored.
There is substantial variation in the handling of include lines
by different implementations. However, there is enough
commonality for the standard to be able to specify a minimum set
of requirements that allow the feature to be used portably. Known
variations have been explicitly called out as unspecified
behavior in the description.
The System V dynamic dependency feature was not included. It
would support:
cat: $$@.c
that would expand to;
cat: cat.c
This feature exists only in the new version of System V make and,
while useful, is not in wide usage. This means that macros are
expanded twice for prerequisites: once at makefile parse time and
once at target update time.
Consideration was given to adding metarules to the POSIX make.
This would make %.o: %.c the same as .c.o:. This is quite useful
and available from some vendors, but it would cause too many
changes to this make to support. It would have introduced rule
chaining and new substitution rules. However, the rules for
target names have been set to reserve the '%' and '"' characters.
These are traditionally used to implement metarules and quoting
of target names, respectively. Implementors are strongly
encouraged to use these characters only for these purposes.
A request was made to extend the suffix delimiter character from
a <period> to any character. The metarules feature in newer makes
solves this problem in a more general way. This volume of
POSIX.1‐2017 is staying with the more conservative historical
definition.
The standard output format for the -p option is not described
because it is primarily a debugging option and because the format
is not generally useful to programs. In historical
implementations the output is not suitable for use in generating
makefiles. The -p format has been variable across historical
implementations. Therefore, the definition of -p was only to
provide a consistently named option for obtaining make script
debugging information.
Some historical implementations have not cleared the suffix list
with -r.
Implementations should be aware that some historical applications
have intermixed target_name and macro=value operands on the
command line, expecting that all of the macros are processed
before any of the targets are dealt with. Conforming applications
do not do this, but some backwards-compatibility support may be
warranted.
Empty inference rules are specified with a <semicolon> command
rather than omitting all commands, as described in an early
proposal. The latter case has no traditional meaning and is
reserved for implementation extensions, such as in GNU make.
Earlier versions of this standard defined comment lines only as
lines with '#' as the first character. Many places then talked
about comments, blank lines, and empty lines; but some places
inadvertently only mentioned comments when blank lines and empty
lines had also been accepted in all known implementations. The
standard now defines comment lines to be blank lines, empty
lines, and lines starting with a '#' character and explictily
lists cases where blank lines and empty lines are not acceptable.
On most historic systems, the make utility considered a target
with a prerequisite that had an identical timestamp as up-to-
date. The HP-UX implementation of make treated it as out-of-date.
The standard now allows either behavior, but implementations are
encouraged to follow the example set by HP-UX. This is
especially important on file systems where the timestamp
resolution is the minimum (1 second) required by the standard.
All implementations of make should make full use of the finest
timestamp resolution available on the file systems holding
targets and prerequisites to ensure that targets are up-to-date
even for prerequisite files with timestamps that were updated
within the same second. However, if the timestamp resolutions of
the file systems containing a target and a prerequisite are
different, the timestamp with the more precise resolution should
be rounded down to the resolution of the less precise timestamp
for the comparison.
Some implementations of make include an export directive to add
specified make variables to the environment. This may be
considered for standardization in a future version.
A future version of this standard may require that macro
expansions using the forms $(string1:[op]%[os]=[np][%][ns]) or
${string1:[op]%[os]=[np][%][ns]} are treated as pattern macro
expansions.
Chapter 2, Shell Command Language, ar(1p), c99(1p), get(1p),
lex(1p), sccs(1p), sh(1p), yacc(1p)
The Base Definitions volume of POSIX.1‐2017, Section 6.1,
Portable Character Set, Chapter 8, Environment Variables, Section
12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2017, exec(1p),
system(3p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The
Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be
obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 MAKE(1P)
Pages that refer to this page: c99(1p), sccs(1p)
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