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

NAME

       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.1‐2008, 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.1‐2008,   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 "$1" 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 "$1" to "$9", inclusive. The
string "$0" is replaced with the name of the macro. The string "$#" 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 is the exit
code. The default is zero. It shall be an error to specify an argument
containing any non-numeric characters.

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 first argument shall be taken as a template for creating an empty file, with
trailing 'X' characters replaced with characters from the portable filename
character set. The behavior is unspecified if the first argument does not end in
at least six 'X' characters. If a temporary file is successfully created, then
the defining text of the macro shall be the name of the new file. The user ID
of the file shall be set to the effective user ID of the process. The group ID
of the file shall be set to the group ID of the file's parent directory or to
the effective group ID of the process. The file access permission bits are set
such that only the owner can both read and write the file, regardless of the
current umask of the process. If a file could not be created, 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  "${"  in  a  macro definition as two literal
       characters. However, this sequence is left unspecified so that implementations  may  offer
       extensions  such as "${11}" 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.

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2013 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX),  The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/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 .