M4(1) M4(1)
NAME
m4 - macro processor
SYNOPSIS
m4 [ files ]
DESCRIPTION
M4 is a macro processor intended as a front end for Rat-
for, 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 pro-
cessed 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 alphabetic letters, dig-
its, 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 col-
lected by searching for a matching right parenthesis.
Macro evaluation proceeds normally 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.
M4 makes available the following built-in macros. They
may be redefined, but once this is done the original mean-
ing 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.
1
M4(1) M4(1)
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.
changequote
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 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 includ-
ing the next newline.
ifelse has three or more arguments. If the first argu-
ment 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 deci-
mal number.
eval evaluates its argument as an arithmetic expres-
sion, using 32-bit arithmetic. Operators
include +, -, *, /, %, ^ (exponentiation); rela-
tionals; parentheses.
len returns the number of characters in its argu-
ment.
index returns the position in its first argument where
the second argument begins (zero origin), or -1
if the second argument does not occur.
2
M4(1) M4(1)
substr returns a substring of its first argument. The
second argument is a zero origin number select-
ing the first character; the third argument
indicates the length of the substring. A miss-
ing third argument is taken to be large enough
to extend to the end of the first string.
translit transliterates the characters in its first argu-
ment 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.
SEE ALSO
B. W. Kernighan and D. M. Ritchie, The M4 Macro Processor
3