m4(1) General Commands Manual m4(1)
m4 - macro processor
m4 [ -Dname[=value]] [-Uname] [files ...]
m4 is a macro processor intended as a front end for 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. Each of the optional argument files is processed in order.
Macro calls have the form
name(arg1,arg2, . . . , argn)
The `(' must immediately follow the name of the macro. If a defined macro name is not followed by a `(', it is deemed to have no argu-
ments. Leading unquoted blanks, tabs, and newlines are ignored while collecting arguments. Potential macro names consist of alphabetic
letters, digits, and underscore `_', where the first character is not a digit.
Left and right single quotes (`') are used to quote strings. The value of a quoted string is the string stripped of the quotes.
When a macro name is recognized, its arguments are collected by searching for a matching right parenthesis. Macro evaluation proceeds nor-
mally during the collection of the arguments, and any commas or right parentheses which happen to turn up within the value of a nested call
are as effective as those in the original input text. After argument collection, the value of the macro is pushed back onto the input
stream and rescanned.
Define the symbol name to have some value (or NULL).
-Uname Undefine the symbol name.
m4 makes available the following built-in macros. They may be redefined, but once this is done the original meaning is lost. Their values
are null unless otherwise stated.
define The second argument is installed as the value of the macro whose name is the first argument. Each occurrence of $n in the
replacement text, where n is a digit, is replaced by the n-th argument. Argument 0 is the name of the macro; missing arguments
are replaced by the null string.
undefine removes the definition of the macro named in its argument.
ifdef If the first argument is defined, the value is the second argument, otherwise the third. If there is no third argument, the
value is null.
changecom Change the start and end comment sequences. The default is the pound sign '#' and the newline character. With no arguments com-
ments are turned off. The maximum legnth for a comment marker is five characters.
Change quote characters to the first and second arguments. Changequote without arguments restores the original values (i.e.,
decr Decrements the argument by 1. The argument must be a valid numeric string.
divert m4 maintains 10 output streams, numbered 0-9. The final output is the concatenation of the streams in numerical order; initially
stream 0 is the current stream. The divert macro changes the current output stream to its (digit-string) argument. Output
diverted to a stream other than 0 through 9 is discarded.
undivert causes immediate output of text from diversions named as arguments, or all diversions if no argument. Text may be undiverted
into another diversion. Undiverting discards the diverted text.
defn Returns the quoted definition for each argument. This can be used to rename macro definitions (even for builtin macros).
divnum returns the value of the current output stream.
dnl reads and discards characters up to and including the next newline.
expr This is an alias for eval.
ifelse has three or more arguments. If the first argument is the same string as the second, then the value is the third argument. If
not, and if there are more than four arguments, the process is repeated with arguments 4, 5, 6 and 7. Otherwise, the value is
either the fourth string, or, if it is not present, null.
incr returns the value of its argument incremented by 1. The value of the argument is calculated by interpreting an initial digit-
string as a decimal number.
eval evaluates its argument as an arithmetic expression, using 32-bit arithmetic. Operators include +, -, *, /, %, ^ (exponentia-
tion); relationals; parentheses.
len returns the number of characters in its argument.
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 processing is done.)
index returns the position in its first argument where the second argument begins (zero origin), or -1 if the second argument does not
substr returns a substring of its first argument. The second argument is a zero origin number selecting the first character; the third
argument indicates the length of the substring. A missing third argument is taken to be large enough to extend to the end of the
translit transliterates the characters in its first argument from the set given by the second argument to the set given by the third. No
abbreviations are permitted.
include returns the contents of the file named in the argument.
sinclude is identical to include, except that it says nothing if the file is inaccessible.
syscmd executes the UNIX command given in the first argument. No value is returned.
maketemp fills in a string of XXXXX in its argument with the current process id.
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.
popdef Restores the pushdef'd definition for each argument.
pushdef Takes the same arguments as define, but it saves the definition on a stack for later retrieval by popdef.
shift Returns all but the first argument, the remaining arguments are quoted and pushed back with commas in between. The quoting nul-
lifies the effect of the extra scan that will subsequently be performed.
spaste Similar to paste, except it ignores any errors.
syscal Returns the return value from the last syscmd.
errprint prints its argument on the diagnostic output file.
dumpdef prints current names and definitions, for the named items, or for all if no arguments are given.
unix A pre-defined macro for testing the OS platform.
B. W. Kernighan and D. M. Ritchie, The m4 Macro Processor
An m4 command appeared in Version 6 AT&T UNIX.
Ozan Yigit <firstname.lastname@example.org>
3rd Berkeley Distribution April 14, 1994 m4(1)