M4(1)

NAME
m4 - macro language processor

SYNOPSIS
m4 [-Pg] [ -Dname[=value]] [-I dirname] [-Uname] [-d flags] [-o trfile] [-t name]

DESCRIPTION
The m4 utility is a macro processor that can be used as a front end to any language (e.g., C, ratfor, fortran, lex, and yacc). m4 reads from the standard input and writes the processed text to the standard output.

Macro calls have the form name(argument1[, argument2, ..., argumentN]).

There cannot be any space following the macro name and the open parenthesis (‘(’). If the macro name is not followed by an open parenthesis it is processed with no arguments.

Macro names consist of a leading alphabetic or underscore possibly followed by alphanumeric or underscore characters, e.g., valid macro names match the pattern “[a-zA-Z_][a-zA-Z0-9_]*”.

In arguments to macros, leading unquoted space, tab, and newline (‘\n’) characters are ignored. To quote strings, use left and right single quotes (e.g., ‘ this is a string with a leading space’). You can change the quote characters with the changequote built-in macro.

Most built-ins don't make any sense without arguments, and hence are not recognized as special when not followed by an open parenthesis.

The options are as follows:

-Dname[
    =value] Define the symbol name to have some value (or NULL).

-I dirname
    Add directory dirname to the include path.

-P  Prefixes all m4 builtin macros with the string “m4_”. This changes the macro names “dnl” to “m4_dnl”, “index” to “m4_index”, and so forth.

-Uname
    Undefine the symbol name.

-d flags
    Set trace flags. flags may hold the following:

    a   print macro arguments.

    c   print macro expansion over several lines.

    e   print result of macro expansion.

    f   print filename location.

    l   print line number.

    q   quote arguments and expansion with the current quotes.

    t   start with all macros traced.

    x   number macro expansions.

    V   turn on all options.

    By default, trace is set to "eq".

-g  Activate GNU-m4 compatibility mode. In this mode, changequote with two empty parameters deactivates quotes, translit handles simple character ranges (e.g., a-z), regular expressions mimic emacs behavior, and the number of diversions is unlimited.

-o trfile
    Specify the tracing output file for -t; tracing defaults to printing to stderr.

-t macro
    Turn tracing on for macro.

SYNTAX
m4 provides the following built-in macros. They may be redefined, losing their original meaning. Return values are null unless otherwise stated.

builtin
    Calls a built-in by its name, overriding possible redefinitions.

changecom
    Change the start and end comment sequences. The default is the pound sign (‘#’) and the newline character. With no arguments comments are turned off. The maximum length for a comment marker is five characters.

changequote
    Defines the quote symbols to be the first and second arguments. The symbols may be up to five characters long. If no arguments are given it restores the default open and close single quotes.

decr
    Decrements the argument by 1. The argument must be a valid numeric string.

define
    Define a new macro named by the first argument to have the value of the second argument. Each occurrence of “$n” (where n is 0 through 9) is replaced by the n'th argument. “$0” is the name of the calling macro. Undefined arguments are replaced by a null string. “$#” is replaced by the number of arguments; “$*” is replaced by all arguments comma separated; “$@” is the same as “$*” but all arguments are quoted against further expansion.

defn
    Returns the quoted definition for each argument. This can be used to rename macro definitions (even for built-in macros).

divert
    There are 10 output queues (numbered 0-9). At the end of processing m4 concatenates all the queues in numerical order to produce the final output. Initially the output queue is 0. The divert macro allows you to select a new output queue (an invalid argument passed to divert causes output to be discarded).

divnum
    Returns the current output queue number.

dnl Discard input characters up to and including the next newline.

dumpdef
    Prints the names and definitions for the named items, or for everything if no arguments are passed.

errprint
    Prints the first argument on the standard error output stream.

esyscmd
    Pass its first argument to a shell and returns the shell's standard output. Note that the shell shares its standard input and standard error with m4.

eval
    Computes the first argument as an arithmetic expression using 32-bit arithmetic. Operators are the standard C ternary, arithmetic, logical, shift, relational, bitwise, and parentheses operators. You can specify octal, decimal, and hexadecimal numbers as in C. The second argument (if any) specifies the radix for the result and the third argument (if any) specifies the minimum number of digits in the result.

expr
    This is an alias for eval.

ifdef
    If the macro named by the first argument is defined then return the second argument, otherwise the third. If there is no third argument, the value is NULL. The word "unix" is predefined.

ifelse
    If the first argument matches the second argument then ifelse returns the third argument. If the match fails the three arguments are discarded and the next three arguments are used until there is zero or one arguments left, either this last argument or NULL is returned if no other matches were found.

include
    Returns the contents of the file specified in the first argument. If the file is not found as is, look through the include path: first the directories specified with -I on the command line, then the environment variable M4PATH, as a colon-separated list of directories. Include aborts with an error message if the file cannot be included.

incr
    Increments the argument by 1. The argument must be a valid numeric string.

index
    Returns the index of the second argument in the first argument (e.g., index(the quick brown fox jumped, fox) returns 16). If the second argument is not found index returns -1.

indir
    Indirectly calls the macro whose name is passed as the first arguments, with the remaining arguments passed as first, ... arguments.

len Returns the number of characters in the first argument. Extra arguments are ignored.

m4exit
    Immediately exits with the return value specified by the first argument, 0 if none.

m4wrap
    Allows you to define what happens at the final EOF, usually for cleanup purposes (e.g., m4wrap("cleanup(tempfile)") causes the macro cleanup to be invoked after all other processing is done).

maketemp
    Translates the string “XXXXX” in the first argument with the current process ID leaving other characters alone. This can be used to create unique temporary file names.

paste
    Includes the contents of the file specified by the first argument without any macro processing. Aborts with an error message if the file cannot be included.

patsubst
    Substitutes a regular expression in a string with a replacement string. Usual substitution patterns apply: an ampersand (‘’) is replaced by the string matching the regular expression. The string “\#”, where ‘#’ is a digit, is replaced by the corresponding back-reference.

popdef
    Restores the pushdefed definition for each argument.

pushdef
    Takes the same arguments as define, but it saves the definition on a stack for later retrieval by popdef.

regexp
    Finds a regular expression in a string. If no further arguments are given, it returns the first match position or -1 if no match. If a third argument is provided, it returns the replacement string, with sub-patterns replaced.

shift
    Returns all but the first argument, the remaining arguments are quoted and pushed back with commas in between. The quoting nullifies the effect of the extra scan that will subsequently be performed.

sinclude
    Similar to include, except it ignores any errors.

spaste
    Similar to paste, except it ignores any errors.

substr
    Returns a substring of the first argument starting at the offset specified by the second argument and the length specified by the third argument. If no third argument is present it returns the rest of the string.

syscmd
    Passes the first argument to the shell. Nothing is returned.

sysval
    Returns the return value from the last syscmd.

traceon
    Enables tracing of macro expansions for the given arguments, or for all macros if no argument is given.

traceoff
    Disables tracing of macro expansions for the given arguments, or for all macros if no argument is given.

translit
    Transliterate the characters in the first argument from the set given by the second argument to the set given by the third. You cannot use tr(1) style abbreviations.

undefine
    Removes the definition for the macro specified by the first argument.

undivert
    Flushes the named output queues (or all queues if no arguments).

unix
    A pre-defined macro for testing the OS platform.

__line__
    Returns the current file's line number.

__file__
    Returns the current file's name.

STANDARDS
The m4 utility is expected to be a superset of the xcu5 specification, and includes some extensions also present in GNU m4.

The -s option ( cpp(1)'s #line directives) is currently not supported. Flags -I, -d, -t are non-standard.

The output format of tracing and of dumpdef are not specified in any standard, are likely to change and should not be relied upon. The current format of tracing is closely modelled on GNU m4, to allow autoconf to work.

For portability, one should not use the macros builtin, esycmd, expr, indir, paste, patsubst, regexp, spaste, unix, __line__, __file__.

All builtins do expand without arguments in many other m4.

AUTHORS
Ozan Yigit oz@sis.yorku.ca and Richard A. O'Keefe (ok@cs.rmit.edu.au). GNU-m4 compatibility extensions by Marc Espie espie@cvs.openbsd.org.