m4 provides the following built-in macros. They may be redefined, losing their original meaning. Return values are null unless otherwise stated.
builtin(name)
Calls a built-in by its name, overriding possible redefinitions.
changecom(startcomment, endcomment)
Changes the start comment and end comment sequences. Comment sequences may be up to five characters long. The default values are the hash sign and the newline character.
With no arguments, comments are turned off. With one single argument, the end comment sequence is set to the newline character.
changequote(beginquote, endquote)
Defines the open quote and close quote sequences. Quote sequences may be up to five characters long. The default values are the backquote character and the quote character.
`Here is a quoted string'
With no arguments, the default quotes are restored. With one single argument, the close quote sequence is set to the newline character.
decr(arg)
Decrements the argument arg by 1. The argument arg must be a valid numeric string.
define(name, value)
Define a new macro named by the first argument name to have the value of the second argument value. 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(name, ...)
Returns the quoted definition for each argument. This can be used to rename macro definitions (even for built-in macros).
divert(num)
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(name, ...)
Prints the names and definitions for the named items, or for everything if no arguments are passed.
errprint(msg)
Prints the first argument on the standard error output stream.
esyscmd(cmd)
Passes 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(expr)
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(expr)
This is an alias for eval.
format(formatstring, arg1, ...)
Returns
formatstring with escape sequences substituted with
arg1 and following arguments, in a way similar to
printf(3). This built-in is only available in GNU-m4 compatibility mode, and the only parameters implemented are there for autoconf compatibility: left-padding flag, an optional field width, a maximum field width, *-specified field widths, and the %s and %c data type.
ifdef(name, yes, no)
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(a, b, yes, ...)
If the first argument a matches the second argument b then ifelse() returns the third argument yes. 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(name)
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(arg)
Increments the argument by 1. The argument must be a valid numeric string.
index(string, substring)
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(macro, arg1, ...)
Indirectly calls the macro whose name is passed as the first argument, with the remaining arguments passed as first, ... arguments.
len(arg)
Returns the number of characters in the first argument. Extra arguments are ignored.
m4exit(code)
Immediately exits with the return value specified by the first argument, 0 if none.
m4wrap(todo)
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).
Multiple calls to
m4wrap() get inserted in sequence at the final
EOF.
maketemp(template)
Invokes
mkstemp(3) on the first argument, and returns the modified string. This can be used to create unique temporary file names.
paste(file)
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(string, regexp, replacement)
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(arg, ...)
Restores the pushdefed definition for each argument.
pushdef(macro, def)
Takes the same arguments as define, but it saves the definition on a stack for later retrieval by popdef().
regexp(string, regexp, replacement)
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(arg1, ...)
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(file)
Similar to include, except it ignores any errors.
spaste(file)
Similar to paste(), except it ignores any errors.
substr(string, offset, length)
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(cmd)
Passes the first argument to the shell. Nothing is returned.
sysval
Returns the return value from the last syscmd.
traceon(arg, ...)
Enables tracing of macro expansions for the given arguments, or for all macros if no argument is given.
traceoff(arg, ...)
Disables tracing of macro expansions for the given arguments, or for all macros if no argument is given.
translit(string, mapfrom, mapto)
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(name1, ...)
Removes the definition for the macros specified by its arguments.
undivert(arg, ...)
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.