M4(1)                      POSIX Programmer's Manual                     M4(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
       m4 -- macro processor

SYNOPSIS
       m4 [[-s]] [[-D name[[=val]]]]... [[-U name]]... file...

DESCRIPTION
       The m4 utility is a macro processor that shall read one or more text
       files, process them according to their included macro statements, and
       write the results to standard output.

OPTIONS
       The m4 utility shall conform to the Base Definitions volume of
       POSIX.1-2017, Section 12.2, Utility Syntax Guidelines, except that the
       order of the -D and -U options shall be significant, and options can be
       interspersed with operands.

       The following options shall be supported:

       -s        Enable line synchronization output for the c99 preprocessor
                 phase (that is, #line directives).

       -D name[[=val]]
                 Define name to val or to null if =val is omitted.

       -U name   Undefine name.

OPERANDS
       The following operand shall be supported:

       file      A pathname of a text file to be processed. If no file is
                 given, or if it is ''--'', the standard input shall be read.

STDIN
       The standard input shall be a text file that is used if no file operand
       is given, or if it is ''--''.

INPUT FILES
       The input file named by the file operand shall be a text file.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of m4:

       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.

       NLSPATH   Determine the location of message catalogs for the processing
                 of LC__MESSAGES.

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       The standard output shall be the same as the input files, after being
       processed for macro expansion.

STDERR
       The standard error shall be used to display strings with the errprint
       macro, macro tracing enabled by the traceon macro, the defined text for
       macros written by the dumpdef macro, or for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       The m4 utility shall compare each token from the input against the set
       of built-in and user-defined macros. If the token matches the name of a
       macro, then the token shall be replaced by the macro's defining text,
       if any, and rescanned for matching macro names. Once no portion of the
       token matches the name of a macro, it shall be written to standard
       output. Macros may have arguments, in which case the arguments shall be
       substituted into the defining text before it is rescanned.

       Macro calls have the form:


           name(arg1, arg2, ..., argn)

       Macro names shall consist of letters, digits, and underscores, where
       the first character is not a digit. Tokens not of this form shall not
       be treated as macros.

       The application shall ensure that the <left-parenthesis> immediately
       follows the name of the macro. If a token matching the name of a macro
       is not followed by a <left-parenthesis>, it is handled as a use of that
       macro without arguments.

       If a macro name is followed by a <left-parenthesis>, its arguments are
       the <comma>-separated tokens between the <left-parenthesis> and the
       matching <right-parenthesis>.  Unquoted white-space characters
       preceding each argument shall be ignored. All other characters,
       including trailing white-space characters, are retained.  <comma>
       characters enclosed between <left-parenthesis> and <right-parenthesis>
       characters do not delimit arguments.

       Arguments are positionally defined and referenced. The string ""$$11"" in
       the defining text shall be replaced by the first argument. Systems
       shall support at least nine arguments; only the first nine can be
       referenced, using the strings ""$$11"" to ""$$99"", inclusive. The string ""$$00""
       is replaced with the name of the macro. The string ""$$##"" is replaced by
       the number of arguments as a string. The string ""$$**"" is replaced by a
       list of all of the arguments, separated by <comma> characters. The
       string ""$$@@"" is replaced by a list of all of the arguments separated by
       <comma> characters, and each argument is quoted using the current left
       and right quoting strings. The string ""$${{"" produces unspecified
       behavior.

       If fewer arguments are supplied than are in the macro definition, the
       omitted arguments are taken to be null. It is not an error if more
       arguments are supplied than are in the macro definition.

       No special meaning is given to any characters enclosed between matching
       left and right quoting strings, but the quoting strings are themselves
       discarded. By default, the left quoting string consists of a grave
       accent (backquote) and the right quoting string consists of an acute
       accent (single-quote); see also the changequote macro.

       Comments are written but not scanned for matching macro names; by
       default, the begin-comment string consists of the <number-sign>
       character and the end-comment string consists of a <newline>.  See also
       the changecom and dnl macros.

       The m4 utility shall make available the following built-in macros. They
       can be redefined, but once this is done the original meaning is lost.
       Their values shall be null unless otherwise stated. In the descriptions
       below, the term defining text refers to the value of the macro: the
       second argument to the define macro, among other things. Except for the
       first argument to the eval macro, all numeric arguments to built-in
       macros shall be interpreted as decimal values. The string values
       produced as the defining text of the decr, divnum, incr, index, len,
       and sysval built-in macros shall be in the form of a decimal-constant
       as defined in the C language.

       changecom The changecom macro shall set the begin-comment and end-
                 comment strings. With no arguments, the comment mechanism
                 shall be disabled. With a single non-null argument, that
                 argument shall become the begin-comment and the <newline>
                 shall become the end-comment string. With two non-null
                 arguments, the first argument shall become the begin-comment
                 string and the second argument shall become the end-comment
                 string. The behavior is unspecified if either argument is
                 provided but null. Systems shall support comment strings of
                 at least five characters.

       changequote
                 The changequote macro shall set the begin-quote and end-quote
                 strings. With no arguments, the quote strings shall be set to
                 the default values (that is, `'). The behavior is unspecified
                 if there is a single argument or either argument is null.
                 With two non-null arguments, the first argument shall become
                 the begin-quote string and the second argument shall become
                 the end-quote string. Systems shall support quote strings of
                 at least five characters.

       decr      The defining text of the decr macro shall be its first
                 argument decremented by 1. It shall be an error to specify an
                 argument containing any non-numeric characters.  The behavior
                 is unspecified if decr is not immediately followed by a
                 <left-parenthesis>.

       define    The second argument shall become the defining text of the
                 macro whose name is the first argument. It is unspecified
                 whether the define macro deletes all prior definitions of the
                 macro named by its first argument or preserves all but the
                 current definition of the macro.  The behavior is unspecified
                 if define is not immediately followed by a <left-
                 parenthesis>.

       defn      The defining text of the defn macro shall be the quoted
                 definition (using the current quoting strings) of its
                 arguments. The behavior is unspecified if defn is not
                 immediately followed by a <left-parenthesis>.

       divert    The m4 utility maintains nine temporary buffers, numbered 1
                 to 9, inclusive.  When the last of the input has been
                 processed, any output that has been placed in these buffers
                 shall be written to standard output in buffer-numerical
                 order. The divert macro shall divert future output to the
                 buffer specified by its argument. Specifying no argument or
                 an argument of 0 shall resume the normal output process.
                 Output diverted to a stream with a negative number shall be
                 discarded. Behavior is implementation-defined if a stream
                 number larger than 9 is specified. It shall be an error to
                 specify an argument containing any non-numeric characters.

       divnum    The defining text of the divnum macro shall be the number of
                 the current output stream as a string.

       dnl       The dnl macro shall cause m4 to discard all input characters
                 up to and including the next <newline>.

       dumpdef   The dumpdef macro shall write the defined text to standard
                 error for each of the macros specified as arguments, or, if
                 no arguments are specified, for all macros.

       errprint  The errprint macro shall write its arguments to standard
                 error. The behavior is unspecified if errprint is not
                 immediately followed by a <left-parenthesis>.

       eval      The eval macro shall evaluate its first argument as an
                 arithmetic expression, using signed integer arithmetic with
                 at least 32-bit precision. At least the following C-language
                 operators shall be supported, with precedence, associativity,
                 and behavior as described in Section 1.1.2.1, Arithmetic
                 Precision and Operations:


                     ()
                     unary +
                     unary -
                     ~

                     !
                     binary *
                     /
                     %
                     binary +
                     binary -
                     <<
                     >>
                     <
                     <=
                     >
                     >=
                     ==
                     !=
                     binary &
                     ^
                     |
                     &&
                     ||

                 Systems shall support octal and hexadecimal numbers as in the
                 ISO C standard.  The second argument, if specified, shall set
                 the radix for the result; if the argument is blank or
                 unspecified, the default is 10. Behavior is unspecified if
                 the radix falls outside the range 2 to 36, inclusive. The
                 third argument, if specified, sets the minimum number of
                 digits in the result. Behavior is unspecified if the third
                 argument is less than zero. It shall be an error to specify
                 the second or third argument containing any non-numeric
                 characters. The behavior is unspecified if eval is not
                 immediately followed by a <left-parenthesis>.

       ifdef     If the first argument to the ifdef macro is defined, the
                 defining text shall be the second argument.  Otherwise, the
                 defining text shall be the third argument, if specified, or
                 the null string, if not. The behavior is unspecified if ifdef
                 is not immediately followed by a <left-parenthesis>.

       ifelse    The ifelse macro takes three or more arguments. If the first
                 two arguments compare as equal strings (after macro expansion
                 of both arguments), the defining text shall be the third
                 argument. If the first two arguments do not compare as equal
                 strings and there are three arguments, the defining text
                 shall be null. If the first two arguments do not compare as
                 equal strings and there are four or five arguments, the
                 defining text shall be the fourth argument. If the first two
                 arguments do not compare as equal strings and there are six
                 or more arguments, the first three arguments shall be
                 discarded and processing shall restart with the remaining
                 arguments. The behavior is unspecified if ifelse is not
                 immediately followed by a <left-parenthesis>.

       include   The defining text for the include macro shall be the contents
                 of the file named by the first argument. It shall be an error
                 if the file cannot be read. The behavior is unspecified if
                 include is not immediately followed by a <left-parenthesis>.

       incr      The defining text of the incr macro shall be its first
                 argument incremented by 1. It shall be an error to specify an
                 argument containing any non-numeric characters.  The behavior
                 is unspecified if incr is not immediately followed by a
                 <left-parenthesis>.

       index     The defining text of the index macro shall be the first
                 character position (as a string) in the first argument where
                 a string matching the second argument begins (zero origin),
                 or -1 if the second argument does not occur.  The behavior is
                 unspecified if index is not immediately followed by a <left-
                 parenthesis>.

       len       The defining text of the len macro shall be the length (as a
                 string) of the first argument.  The behavior is unspecified
                 if len is not immediately followed by a <left-parenthesis>.

       m4exit    Exit from the m4 utility. If the first argument is specified,
                 it shall be the exit code. If no argument is specified, the
                 exit code shall be zero. It shall be an error to specify an
                 argument containing any non-numeric characters. If the first
                 argument is zero or no argument is specified, and an error
                 has previously occurred (for example, a file operand that
                 could not be opened), it is unspecified whether the exit
                 status is zero or non-zero.

       m4wrap    The first argument shall be processed when EOF is reached. If
                 the m4wrap macro is used multiple times, the arguments
                 specified shall be processed in the order in which the m4wrap
                 macros were processed. The behavior is unspecified if m4wrap
                 is not immediately followed by a <left-parenthesis>.

       maketemp  The defining text shall be the first argument, with any
                 trailing 'X' characters replaced with the current process ID
                 as a string.  The behavior is unspecified if maketemp is not
                 immediately followed by a <left-parenthesis>.

       mkstemp   The defining text shall be as if it were the resulting
                 pathname after a successful call to the mkstemp() function
                 defined in the System Interfaces volume of POSIX.1-2017
                 called with the first argument to the macro invocation. If a
                 file is created, that file shall be closed.  If a file could
                 not be created, the m4 utility shall write a diagnostic
                 message to standard error and shall continue processing input
                 but its final exit status shall be non-zero; the defining
                 text of the macro shall be the empty string. The behavior is
                 unspecified if mkstemp is not immediately followed by a
                 <left-parenthesis>.

       popdef    The popdef macro shall delete the current definition of its
                 arguments, replacing that definition with the previous one.
                 If there is no previous definition, the macro is undefined.
                 The behavior is unspecified if popdef is not immediately
                 followed by a <left-parenthesis>.

       pushdef   The pushdef macro shall be equivalent to the define macro
                 with the exception that it shall preserve any current
                 definition for future retrieval using the popdef macro. The
                 behavior is unspecified if pushdef is not immediately
                 followed by a <left-parenthesis>.

       shift     The defining text for the shift macro shall be a comma-
                 separated list of its arguments except the first one. Each
                 argument shall be quoted using the current quoting strings.
                 The behavior is unspecified if shift is not immediately
                 followed by a <left-parenthesis>.

       sinclude  The sinclude macro shall be equivalent to the include macro,
                 except that it shall not be an error if the file is
                 inaccessible.  The behavior is unspecified if sinclude is not
                 immediately followed by a <left-parenthesis>.

       substr    The defining text for the substr macro shall be the substring
                 of the first argument beginning at the zero-offset character
                 position specified by the second argument. The third
                 argument, if specified, shall be the number of characters to
                 select; if not specified, the characters from the starting
                 point to the end of the first argument shall become the
                 defining text. It shall not be an error to specify a starting
                 point beyond the end of the first argument and the defining
                 text shall be null. It shall be an error to specify an
                 argument containing any non-numeric characters.  The behavior
                 is unspecified if substr is not immediately followed by a
                 <left-parenthesis>.

       syscmd    The syscmd macro shall interpret its first argument as a
                 shell command line. The defining text shall be the string
                 result of that command. The string result shall not be
                 rescanned for macros while setting the defining text. No
                 output redirection shall be performed by the m4 utility. The
                 exit status value from the command can be retrieved using the
                 sysval macro. The behavior is unspecified if syscmd is not
                 immediately followed by a <left-parenthesis>.

       sysval    The defining text of the sysval macro shall be the exit value
                 of the utility last invoked by the syscmd macro (as a
                 string).

       traceon   The traceon macro shall enable tracing for the macros
                 specified as arguments, or, if no arguments are specified,
                 for all macros. The trace output shall be written to standard
                 error in an unspecified format.

       traceoff  The traceoff macro shall disable tracing for the macros
                 specified as arguments, or, if no arguments are specified,
                 for all macros.

       translit  The defining text of the translit macro shall be the first
                 argument with every character that occurs in the second
                 argument replaced with the corresponding character from the
                 third argument. If no replacement character is specified for
                 some source character because the second argument is longer
                 than the third argument, that character shall be deleted from
                 the first argument in translit's defining text. The behavior
                 is unspecified if the ''--'' character appears within the second
                 or third argument anywhere besides the first or last
                 character. The behavior is unspecified if the same character
                 appears more than once in the second argument. The behavior
                 is unspecified if translit is not immediately followed by a
                 <left-parenthesis>.

       undefine  The undefine macro shall delete all definitions (including
                 those preserved using the pushdef macro) of the macros named
                 by its arguments. The behavior is unspecified if undefine is
                 not immediately followed by a <left-parenthesis>.

       undivert  The undivert macro shall cause immediate output of any text
                 in temporary buffers named as arguments, or all temporary
                 buffers if no arguments are specified. Buffers can be
                 undiverted into other temporary buffers.  Undiverting shall
                 discard the contents of the temporary buffer. The behavior is
                 unspecified if an argument contains any non-numeric
                 characters.

EXIT STATUS
       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred

       If the m4exit macro is used, the exit value can be specified by the
       input file.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       The defn macro is useful for renaming macros, especially built-ins.

       Since eval defers to the ISO C standard, some operations have undefined
       behavior. In some implementations, division or remainder by zero cause
       a fatal signal, even if the division occurs on the short-circuited
       branch of ""&&&&"" or ""||||"".  Any operation that overflows in signed
       arithmetic produces undefined behavior. Likewise, using the shift
       operators with a shift amount that is not positive and smaller than the
       precision is undefined, as is shifting a negative number to the right.
       Historically, not all implementations obeyed C-language precedence
       rules: ''~~'' and ''!!''  were lower than ''====''; ''===='' and ''!!=='' were not lower
       than ''<<''; and ''||'' was not lower than ''^^''; the liberal use of ""(())"" can
       force the desired precedence even with these non-compliant
       implementations. Furthermore, some traditional implementations treated
       ''^^'' as an exponentiation operator, although most implementations now
       use ""****"" as an extension for this purpose.

       When a macro has been multiply defined via the pushdef macro, it is
       unspecified whether the define macro will alter only the most recent
       definition (as though by popdef and pushdef), or replace the entire
       stack of definitions with a single definition (as though by undefine
       and pushdef).  An application desiring particular behavior for the
       define macro in this case can redefine it accordingly.

       Applications should use the mkstemp macro instead of the obsolescent
       maketemp macro for creating temporary files.

EXAMPLES
       If the file m4src contains the lines:


           The value of `VER' is "VER".
           ifdef(`VER', ``VER'' is defined to be VER., VER is not defined.)
           ifelse(VER, 1, ``VER'' is `VER'.)
           ifelse(VER, 2, ``VER'' is `VER'., ``VER'' is not 2.)
           end

       then the command


           m4 m4src

       or the command:


           m4 -U VER m4src

       produces the output:


           The value of VER is "VER".
           VER is not defined.

           VER is not 2.
           end

       The command:


           m4 -D VER m4src

       produces the output:


           The value of VER is "".
           VER is defined to be .

           VER is not 2.
           end

       The command:


           m4 -D VER=1 m4src

       produces the output:


           The value of VER is "1".
           VER is defined to be 1.
           VER is 1.
           VER is not 2.
           end

       The command:


           m4 -D VER=2 m4src

       produces the output:


           The value of VER is "2".
           VER is defined to be 2.

           VER is 2.
           end

RATIONALE
       Historic System V-based behavior treated ""$${{"" in a macro definition as
       two literal characters. However, this sequence is left unspecified so
       that implementations may offer extensions such as ""$${{1111}}"" meaning the
       eleventh positional parameter. Macros can still be defined with
       appropriate uses of nested quoting to result in a literal ""$${{"" in the
       output after rescanning removes the nested quotes.

       In the translit built-in, historic System V-based behavior treated ''--''
       as a literal; GNU behavior treats it as a range. This version of the
       standard allows either behavior.

FUTURE DIRECTIONS
       None.

SEE ALSO
       c99

       The Base Definitions volume of POSIX.1-2017, Chapter _8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

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                                M4(1)
