m4 - macro processor
m4 [options<b>] [files<b>]
The m4 command is a macro processor intended as a front end for C,
assembler, and other languages. Each of the argument files is processed
in order; if there are no files, or if a file name is -, the standard
input is read. The processed text is written on the standard output. m4
processes supplementary code set characters in comments and literals
according to the locale specified in the LC_CTYPE environment variable
[see LANG on environ(5)].
The options and their effects are as follows:
-e Operate interactively. Interrupts are ignored and the output is
-s Enable line sync output for the C preprocessor (#line ...)
-Bint Change the size of the push-back and argument collection buffers
from the default of 4,096.
-Hint Change the size of the symbol table hash array from the default
of 199. The size should be prime.
-Sint Change the size of the call stack from the default of 100 slots.
Macros take three slots, and non-macro arguments take one.
-Tint Change the size of the token buffer from the default of 512
To be effective, the above flags must appear before any file names and
before any -D or -U flags:
Defines name to val or to null in val's absence.
-Uname undefines name.
Macro calls have the form:
name(arg1,arg2, ..., argn)
The ( must immediately follow the name of the macro. If the name of a
defined macro is not followed by a (, it is deemed to be a call of that
macro with no arguments. Potential macro names consist of alphanumeric
characters and underscore (_), where the first character is not a digit.
Leading unquoted blanks, tabs, and new-lines are ignored while collecting
arguments. 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. If fewer arguments are supplied than
are in the macro definition, the trailing arguments are taken to be null.
Macro evaluation proceeds normally during the collection of the
arguments, and any commas or right parentheses that 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. These macros 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; $# is replaced by
the number of arguments; $* is replaced by a list of all the
arguments separated by commas; $@ is like $*, but each
argument is quoted (with the current quotes).
undefine removes the definition of the macro named in its argument.
defn returns the quoted definition of its argument(s). It is
useful for renaming macros, especially built-ins.
pushdef like define, but saves any previous definition.
popdef removes current definition of its argument(s), exposing the
previous one, if any.
ifdef If the first argument to the ifdef macro is defined and it
is not defined to be zero, the defining text is the second
argument. Otherwise, the defining text is the third
argument, if specified, or the null string, if not. The
word unix is predefined.
shift returns all but its first argument. The other arguments are
quoted and pushed back with commas in between. The quoting
nullifies the effect of the extra scan that will
subsequently be performed.
changequote change quote symbols to the first and second arguments. The
symbols may be up to five characters long. changequote
without arguments restores the original values (that is,
changecom change left and right comment markers from the default # and
new-line. With no arguments, the comment mechanism is
effectively disabled. With one argument, the left marker
becomes the argument and the right marker becomes new-line.
With two arguments, both markers are affected. Comment
markers may be up to five characters long.
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 (digitstring)
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
divnum returns the value of the current output stream.
dnl reads and discards characters up to and including the next
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.
decr returns the value of its argument decremented by 1.
eval evaluates its argument as an arithmetic expression, using
32-bit arithmetic. Operators include +, -, *, /, %, **
(exponentiation), bitwise &, |, ^, and ~; relationals;
parentheses. Octal and hex numbers may be specified as in
C. The second argument specifies the radix for the result;
the default is 10. The third argument may be used to
specify the minimum number of digits in the result.
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 System command given in the first
argument. No value is returned.
sysval is the return code from the last call to syscmd.
maketemp fills in a string of XXXXX in its argument with the current
m4exit causes immediate exit from m4. Argument 1, if given, is the
exit code; the default is 0.
m4wrap The first argument will be processed when EOF is reached. If
the m4wrap macro is used multiple times, the arguments
specified will be processed in the order in which the m4wrap
macros were processed.
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.
traceon with no arguments, turns on tracing for all macros
(including built-ins). Otherwise, turns on tracing for
traceoff turns off trace globally and for any macros specified.
Macros specifically traced by traceon can be untraced only
by specific calls to traceoff.
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