m4 - macro language processor
m4 [-d flags] [-t name] [-o filename] [-g] [-s]
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
the standard input and writes the processed text to the
Macro calls have the form name(argument1[, argument2, ...,
There cannot be any space following the macro name and the
(`('). If the macro name is not followed by an open
is processed with no arguments.
Macro names consist of a leading alphabetic or underscore
by alphanumeric or underscore characters, e.g., valid
match the pattern ``[a-zA-Z_][a-zA-Z0-9_]*''.
In arguments to macros, leading unquoted space, tab, and
characters are ignored. To quote strings, use left and
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:
Define the symbol name to have some value (or NULL).
-Uname Undefine the symbol name.
Add directory dirname to the include path.
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".
Send trace output to filename.
Turn tracing on for macro.
-g Activate GNU-m4 compatibility mode. In this mode,
with two empty parameters deactivates quotes,
simple character ranges (e.g., a-z), regular expressions mimic
emacs behavior, and the number of diversions is unlimited.
-s Output line synchronization directives, suitable for
m4 provides the following built-in macros. They may be redefined, losing
their original meaning. Return values are null unless otherwise stated.
Calls a built-in by its name, overriding possible redefinitions.
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.
Defines the quote symbols to be the first and
The symbols may be up to five characters long. If
no arguments are given it restores the default
close single quotes.
decr(arg) Decrements the argument arg by 1. The argument
arg must be
a valid numeric string.
Define a new macro named by the first argument
name to have
the value of the second argument value. Each
`$n' (where n is 0 through 9) is replaced by
the n'th argument.
`$0' is the name of the calling macro.
are replaced by a null string. `$#' is
the number of arguments; `$*' is replaced by
comma separated; `$@' is the same as `$*' but
are quoted against further expansion.
Returns the quoted definition for each argument. This can
be used to rename macro definitions (even for
divert(num) There are 10 output queues (numbered 0-9). At
the end of
processing m4 concatenates all the queues in
to produce the final output. Initially the
output queue is
0. The divert macro allows you to select a new
(an invalid argument passed to divert causes
output to be
divnum Returns the current output queue number.
dnl Discard input characters up to and including
the next newline.
Prints the names and definitions for the named
items, or for
everything if no arguments are passed.
Prints the first argument on the standard error
Passes its first argument to a shell and returns the shell's
standard output. Note that the shell shares
input and standard error with m4.
eval(expr) Computes the first argument as an arithmetic
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
any) specifies the radix for the result and the
(if any) specifies the minimum number of
digits in the
expr(expr) This is an alias for eval.
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
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
are used until there is zero or one arguments left,
either this last argument or NULL is returned
if no other
matches were found.
Returns the contents of the file specified in
the first argument.
If the file is not found as is, look
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
Returns the index of the second argument in the
(e.g., index(the quick brown fox jumped,
16). If the second argument is not found index
indir(macro, arg1, ...)
Indirectly calls the macro whose name is passed
as the first
argument, with the remaining arguments passed
as first, ...
len(arg) Returns the number of characters in the first
arguments are ignored.
Immediately exits with the return value specified by the
first argument, 0 if none.
Allows you to define what happens at the final
for cleanup purposes (e.g.,
causes the macro cleanup to be invoked after
all other processing
Invokes mkstemp(3) on the first argument, and
modified string. This can be used to create
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
expression. The string `
placed by the corresponding back-reference.
Restores the pushdefed definition for each argument.
Takes the same arguments as define, but it
saves the definition
on a stack for later retrieval by
regexp(string, regexp, replacement)
Finds a regular expression in a string. If no
are given, it returns the first match position or -1
if no match. If a third argument is provided,
the replacement string, with sub-patterns replaced.
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
subsequently be performed.
Similar to include, except it ignores any errors.
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
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.
Enables tracing of macro expansions for the
or for all macros if no argument is given.
Disables tracing of macro expansions for the
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.
Removes the definition for the macros specified
by its arguments.
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.
m4 follows the Single Unix 2 specification, along with a few
taken from gnu-m4.
The -s option (cpp(1)'s #line directives) is currently not
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
The built-ins pushdef and popdef handle macro definitions as
However, define interacts with the stack in an undefined
way. In this
implementation, define replaces the top-most definition only. Other implementations
may erase all definitions on the stack instead.
For portability, one should not use the macros builtin,
indir, paste, patsubst, regexp, spaste, unix, __line__,
All built-ins do expand without arguments in many other m4.
Many other m4 have dire size limitations with respect to
Ozan Yigit <email@example.com> and
Richard A. O'Keefe <firstname.lastname@example.org.OZ.AU>.
GNU-m4 compatibility extensions by
Marc Espie <email@example.com>.
OpenBSD 3.6 January 26, 1993
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