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M4(1P) POSIX Programmer's Manual M4(1P)

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

NAME
m4 - macro processor (DEVELOPMENT)

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 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guide-
lines, except that the order of the -D and -U options shall be significant.

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 IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of international-
ization 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 stan-
dard 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 res-
canned.

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 paren-
thesis and the matching right parenthesis. Unquoted <blank>s and <newline>s preceding each argument shall be ignored. All
other characters, including trailing <blank>s and <newline>s, are retained. Commas enclosed between left 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 "$*" is replaced by a list of all of the arguments, separated by commas. The string
"$@" is replaced by a list of all of the arguments separated by commas, and each argument is quoted using the current
left and right quoting strings.

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 ( '`' ) and the right
quoting string consists of an acute accent ( '" ); see also the changequote macro.

Comments are written but not scanned for matching macro names; by default, the begin-comment string consists of the num-
ber 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 defin-
ing 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 argument, that argument shall become the begin-comment string and the <newline>
shall become the end-comment string. With two arguments, the first argument shall become the begin-comment string
and the second argument shall become the end-comment string. 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, `'). With a single argument, that argument shall become the begin-quote
string and the <newline> shall become the end-quote string. With two 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.

define The second argument shall become the defining text of the macro whose name is the first argument.

defn The defining text of the defn macro shall be the quoted definition (using the current quoting strings) of its
arguments.

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-numeri-
cal 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 other than 0 to 9
shall be discarded. 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.

eval The eval macro shall evaluate its first argument as an arithmetic expression, using 32-bit signed integer arith-
metic. All of the C-language operators shall be supported, except for:

[]
->
++
--
(type)
unary *
sizeof,
.
?:
unary &

and all assignment operators. It shall be an error to specify any of these operators. Precedence and associativity shall
be as in the ISO C standard. 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; the default is 10. The third argument, if specified, sets
the minimum number of digits in the result. It shall be an error to specify the second or third argument containing any
non-numeric characters.

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.

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 argu-
ments 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.

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.

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.

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.

len The defining text of the len macro shall be the length (as a string) of the first argument.

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 argu-
ments specified shall be processed in the order in which the m4wrap macros were processed.

maketemp
The defining text shall be the first argument, with any trailing 'X' characters replaced with the current process
ID as a string.

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.

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.

shift The defining text for the shift macro shall be all of its arguments except for the first one.

sinclude
The sinclude macro shall be equivalent to the include macro, except that it shall not be an error if the file is
inaccessible.

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.

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. No output redirection shall be performed by the m4 utility. The exit status value from the
command can be retrieved using the sysval macro.

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.

undefine
The undefine macro shall delete all definitions (including those preserved using the pushdef macro) of the macros
named by its arguments.

undivert
The undivert macro shall cause immediate output of any text in temporary buffers named as arguments, or all tempo-
rary buffers if no arguments are specified. Buffers can be undiverted into other temporary buffers. Undiverting
shall discard the contents of the temporary buffer. It shall be an error to specify an argument containing 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.

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
None.

FUTURE DIRECTIONS
None.