name(arg1,arg2, . . . , argn)

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. The word unix is predefined on UNIX versions of m4.

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.

divnum

returns the value of the current output stream.

dnl

reads and discards characters up to and including the next newline.

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 +, −, ∗, /, %, ^ (exponentiation); relationals; parentheses.

len

returns the number of characters in its argument.

index

returns the position in its first argument where the second argument begins (zero origin), or −1 if the second argument does not occur.

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 first string.

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.

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.