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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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

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

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

INPUT FILES
       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
       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
       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
       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
       The standard error shall be used only for diagnostic messages.

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

EXTENDED DESCRIPTION
       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).  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 (..oo).  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..oo) expression lib
       refers to the name of the archive library and member..oo 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.  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..oo).  In
               these cases, $@ shall evaluate to libname and $% shall evaluate
               to member..oo.  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..oo) and the s2.a rule, the internal macros
       shall be defined as:

       $<      member..ss22

       $*      member

       $@      lib

       $?      member..ss22

       $%      member..oo

   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 CCCC, CFLAGS, YACC,
       YFLAGS, LEX, LFLAGS, LDFLAGS, and the ..cc, ..yy, 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
       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
       Default.

       The following sections are informative.

APPLICATION USAGE
       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 kk 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 ..oo.  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
        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
       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.

FUTURE DIRECTIONS
       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
       Chapter _2, Shell Command Language, ar, c99, get, lex, sccs, sh, yacc

       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, system()

COPYRIGHT
       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(1)
