make(1p) — Linux manual page

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

MAKE(1P)                POSIX Programmer's Manual               MAKE(1P)

PROLOG         top

       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.

NAME         top

       make — maintain, update, and regenerate groups of programs
       (DEVELOPMENT)

SYNOPSIS         top

       make [-einpqrst] [-f makefile]... [-k|-S] [macro=value...]
           [target_name...]

DESCRIPTION         top

       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.

OPTIONS         top

       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.

OPERANDS         top

       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.

STDIN         top

       The standard input shall be used only if the makefile option-
       argument is '-'.  See the INPUT FILES section.

INPUT FILES         top

       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.

ENVIRONMENT VARIABLES         top

       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.

ASYNCHRONOUS EVENTS         top

       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.

STDOUT         top

       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.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       Files can be created when the -t option is present. Additional
       files can also be created by the utilities invoked by make.

EXTENDED DESCRIPTION         top

       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

EXIT STATUS         top

       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.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       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)

EXAMPLES         top

        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

RATIONALE         top

       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: [email protected]

       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.

FUTURE DIRECTIONS         top

       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.

SEE ALSO         top

       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)

COPYRIGHT         top

       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)

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