m4 - macro processor
m4 [ files ]
M4 is a macro processor intended as a front end for Ratfor, C, and other languages. Each
of the argument files is processed in order; if there are no arguments, or if an argument
is `-', the standard input is read. The processed text is written on the standard output.
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 arguments. Leading unquoted blanks, tabs, and
newlines are ignored while collecting arguments. Potential macro names consist of alpha-
betic 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 normally during the collection of the argu-
ments, 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 collec-
tion, the value of the macro is pushed back onto the input stream and rescanned.
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. The word unix is
predefined on UNIX versions of m4.
Change quote characters to the first and second arguments. Changequote without
arguments restores the original values (i.e., `').
divert M4 maintains 10 output streams, numbered 0-9. The final output is the concate-
nation 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 dis-
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. Oth-
erwise, 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 inaccessi-
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.
B. W. Kernighan and D. M. Ritchie, The M4 Macro Processor