M4(1) BSD General Commands Manual M4(1)NAMEm4 — macro language processor
SYNOPSISm4 [-d flags] [-t name] [-gs] [-D name[=value]] [-U name] [-I dirname]
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). The m4 utility
reads from the standard input and writes the processed text to the stan‐
Macro calls have the form name(argument1[, argument2, ..., argumentN]).
There cannot be any space following the macro name and the open parenthe‐
sis (‘(’). 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 fol‐
lowed 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 do not make any sense without arguments, and hence are not
recognized as special when not followed by an open parenthesis.
The options are as follows:
-s Emit #line directives for cpp(1).
Define the symbol name to have some value (or NULL).
Undefine the symbol name.
Add directory dirname to the include path.
Set trace flags. The flags argument 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.
Turn tracing on for macro.
-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(1) behavior, and the number of diversions is unlimited.
The m4 utility provides the following built-in macros. They may be rede‐
fined, losing their original meaning. Return values are null unless oth‐
builtin Calls a built-in by its name, overriding possible redefini‐
changecom Changes the start and end comment sequences. The default is
the pound sign (‘#’) and the newline character. With no
arguments, the comment sequence is reset to the default, in
GNU m4 mode, 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 argu‐
ments. 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
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 num‐
ber 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
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
divnum Returns the current output queue number.
dnl Discards input characters up to and including the next new‐
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
esyscmd 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 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 argu‐
ment (if any) specifies the minimum number of digits in the
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
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
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. Aborts with an error
message if the file cannot be included.
incr Increments the argument by 1. The argument must be a valid
index Returns the index of the second argument in the first argu‐
ment (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,
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
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 replace‐
ment string. Usual substitution patterns apply: an amper‐
sand (‘&’) 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 defini‐
tion on a stack for later retrieval by popdef.
regexp Finds a regular expression in a string. If no further argu‐
ments 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 spec‐
ified 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
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 argu‐
ments, 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 macros specified by its argu‐
undivert Flushes the named output queues (or all queues if no argu‐
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.
The m4 utility exits 0 on success, and >0 if an error occurs.
The m4exit macro may be used to change the exit status from the input
The m4 utility follows the Version 2 of the Single UNIX Specification
(“SUSv2”), along with a few extensions taken from GNU-m4. Flags -I, -d,
and -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 cur‐
rent format of tracing is closely modeled on GNU-m4, to allow autoconf to
For portability, one should not use the macros builtin, esyscmd, expr,
indir, paste, patsubst, regexp, spaste, unix, __line__, and __file__.
All built-ins do expand without arguments in many other m4 implementa‐
Many other m4 implementations have dire size limitations with respect to
The m4 utility conforms to IEEE Std 1003.1-2001 (“POSIX.1”).
An m4 command appeared in PWB UNIX.
Ozan Yigit ⟨firstname.lastname@example.org⟩ and Richard A. O'Keefe
⟨email@example.com.OZ.AU⟩. GNU-m4 compatibility extensions by Marc Espie
The m4 utility does not recognize multibyte characters.
BSD July 3, 2004 BSD