Command: m4 - macro processor
Syntax: m4 [-D name = value] [-U name]
Flags: -D Define a symbol
-U Undefine a symbol
Example: m4 <m4test # Run M4
M4 is a macro processor intended as a front end for Ratfor, Pascal,
and other languages that do not have a built-in macro processing
capability. M4 reads standard input, the processed text is written on
the standard output.
The options and their effects are as follows:
-D name[=val] Defines name to val, or to null in val's absence.
-U name 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 taken to be a call of that
macro with no arguments, i.e. name(). Potential macro names consist of
alphabetic letters and digits.
Leading unquoted blanks, tabs and newlines 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
When a macro name is recognized, its arguments are collected by
searching for a matching ). 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 which happen to turn up
within the value of a nested call are as effective as those in the
original input text. (This is typically referred as inside-out macro
expansion.) 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 meaning is lost. Their
values are null unless otherwise stated.
define "(name [, val])" the second argument is installed as the
value of the macro whose name is the first argument. If there is no
second argument, the value is null. 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.
defn "(name [, name ...])" returns the quoted definition of its
argument(s). Useful in renaming macros.
undefine "(name [, name ...])" removes the definition of the
macro(s) named. If there is more than one definition for the named
macro, (due to previous use of pushdef) all definitions are removed.
pushdef "(name [, val])" like define, but saves any previous
definition by stacking the current definition.
popdef "(name [, name ...])" removes current definition of its
argument(s), exposing the previous one if any.
ifdef "(name, if-def [, ifnot-def])" 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. A word indicating the
current operating system is predefined. (e.g. unix or vms).
shift "(arg, arg, arg, ...)" 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 "(lqchar, rqchar)" change quote symbols to the first
and second arguments. With no arguments, the quotes are reset back to
the default characters. (i.e., `').
changecom "(lcchar, rcchar)" change left and right comment markers
from the default # and newline. With no arguments, the comment
mechanism is reset back to the default characters. With one argument,
the left marker becomes the argument and the right marker becomes
newline. With two arguments, both markers are affected.
divert "(divnum)" maintains 10 output streams, numbered 0-9.
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 lost.
undivert "([divnum [, divnum ...]])" causes immediate output of
text from diversions named as argument(s), or all diversions if no
argument. Text may be undiverted into another diversion. Undiverting
discards the diverted text. At the end of input processing, M4 forces an
automatic undivert unless is defined.
divnum "()" returns the value of the current output stream.
dnl "()" reads and discards characters up to and including the next
ifelse "(arg, arg, if-same [, ifnot-same | arg, arg ...])" 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 "(num)" 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 "(num)" returns the value of its argument decremented by 1.
eval "(expression)" evaluates its argument as a constant
expression, using integer arithmetic. The evaluation mechanism is very
similar to that of cpp (#if expression). The expression can involve
only integer constants and character constants, possibly connected by
the binary operators
* / % + - >> << < > <= >= == != &
^ | && ||
or the unary operators - ! or tilde or by the ternary operator ? : .
Parentheses may be used for grouping. Octal numbers may be specified as
len "(string)" returns the number of characters in its argument.
index "(search-string, string)" returns the position in its first
argument where the second argument begins (zero origin), or 1 if the
second argument does not occur.
substr "(string, index [, length])" returns a substring of its
first argument. The second argument is a zero origin number selecting
the first character (internally treated as an expression); 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
translit "(source, from [, to])" transliterates the characters in
its first argument from the set given by the second argument to the set
given by the third. If the third argument is shorter than the second,
all extra characters in the second argument are deleted from the first
argument. If the third argument is missing altogether, all characters in
the second argument are deleted from the first argument.
include "(filename)" returns the contents of the file that is named
in the argument.
sinclude "(filename)"is identical to include, except that it says
nothing if the file is inaccessable.
paste "(filename)" returns the contents of the file named in the
argument without any processing, unlike include.
spaste "(filename)" is identical to paste, except that it says
nothing if the file is inaccessibl[De.
syscmd "(command)" executes the UNIX command given in the first
argument. No value is returned.
sysval "()" is the return code from the last call to syscmd.
.PP maketemp '(string)" fills in a string of XXXXXX in its argument
with the current process ID.
m4exit "([exitcode])" causes immediate exit from M4. Argument 1,
if given, is the exit code; the default is 0.
m4wrap "(m4-macro-or-built-n)" argument 1 will be pushed back at
final EOF; example: m4wrap(`dumptable()').
errprint "(str [, str, str, ...])" prints its argument(s) on
stderr. If there is more than one argument, each argument is separated
by a space during the output. An arbitrary number of arguments may be
dumpdef "([name, name, ...])" prints current names and definitions,
for the named items, or for all if no arguments are given.
M4 was written by Ozan S. Yigif.