The m4(1) utility is a macro processor that can be used
as a front end to any language (such as C, ratfor, fortran, lex,
and yacc). The m4(1) utility reads from the standard input
and writes the processed text to the standard output.
Macro calls have the form:
name(argument1[, argument2, ...,] argumentN)
There cannot be any space following the macro name and the open
parentheses '('. If the macro name is not followed by an open
parentheses, it is processed with no arguments.
Macro names consist of a leading alphabetic or underscore,
possibly followed by alphanumeric or underscore characters. Valid
macro names match this pattern: [a-zA-Z_][a-zA-Z0-9_]*.
In arguments to macros, leading unquoted space, tab, and newline
characters are ignored. To quote strings, use left and right single
quotes (for example: ' this is a string with a leading space'). You can change the quote characters with the
changequote built-in macro.
The options are as follows:
-Dname
-Dname=value
Define the symbol name to have some value (or
NULL).
The m4(1) utility provides the following built-in macros.
They can be redefined, losing their original meaning. Return values
are NULL unless otherwise stated.
changecom
Change the start and end comment sequences. The default is the
pound sign (#) and the newline character. With no arguments,
comments are turned off. The maximum length for a comment marker is
five characters.
changequote
Defines the quote symbols to be the first and second arguments.
The symbols can be up to five characters long. If no arguments are
given, it restores the default open and close single quotes.
decr
Decrements the argument by 1. The argument must be a valid
numeric string.
define
Define a new macro named by the first argument to have the
value of the second argument. Each occurrence of $n
(where n is 0 through 9) is replaced by the occurrence of
the argument specified by n. The name of the calling macro
is $0. Undefined arguments are replaced by a NULL string. $# is
replaced by the number of arguments; $* is replaced by all
arguments, comma separated; $@ is the same as $*, but all arguments
are quoted against further expansion.
defn
Returns the quoted definition for each argument. This can be
used to rename macro definitions (even for built-in macros).
divert
There are ten output queues (numbered 0-9). At the end of
processing, m4(1) concatenates all the queues in numerical
order to produce the final output. Initially, the output queue is
0. You can use the divert macro to select a new output queue (an
invalid argument passed to divert causes output to be
discarded).
divnum
Returns the current output queue number.
dnl
Discard input characters up to and including the next
newline.
dumpdef
Prints the names and definitions for the named items, or for
everything if no arguments are passed.
errprint
Prints the first argument on the standard-error output
stream.
eval
Computes the first argument as an arithmetic expression using
32-bit arithmetic. Operators are the standard C ternary,
arithmetic, logical, shift, relational, bitwise, and parentheses
operators. You can specify octal, decimal, and hexadecimal numbers
as in C. The second argument (if there is one) specifies the radix
for the result, and the third argument (if there is one) specifies
the minimum number of digits in the result.
expr
This is an alias for eval.
ifdef
If the macro named by the first argument is defined return the
second argument; otherwise the third. If there is no third
argument, the value is NULL. The word 'unix' is predefined.
ifelse
If the first argument matches the second argument,
ifelse returns the third argument. If the match fails, the
three arguments are discarded and the next three arguments are used
until there is zero or one argument left; either this last argument
or NULL is returned if no other matches were found.
include
Returns the contents of the file specified in the first
argument. Include aborts with an error message if the file cannot
be included.
incr
Increments the argument by 1. The argument must be a valid
numeric string.
index
Returns the index of the second argument in the first argument.
For example, index(the quick brown fox jumped, fox) returns 16. If
the second argument is not found, index returns -1.
len
Returns the number of characters in the first argument. Extra
arguments are ignored.
m4exit
Immediately exits with the return value specified by the first
argument; 0 if none is specified.
m4wrap
Allows you to define what happens at the final EOF, usually for
clean-up purposes. For example, m4wrap("cleanup(tempfile)") causes
the macro cleanup to invoked after all other processing is
done.
maketemp
Translates the string XXXXX in the first argument with the
current process identifier (ID) leaving other characters alone.
This can be used to create unique temporary file names.
paste
Includes the contents of the file specified by the first
argument without any macro processing. Aborts with an error message
if the file cannot be included.
popdef
Restores the definition of an argument that was pushed onto the
stack by pushdef.
pushdef
Takes the same arguments as define, but saves the
definition on a stack for later retrieval by popdef.
shift
Returns all but the first argument; the remaining arguments are
quoted and pushed back with commas separating them. The quoting
nullifies the effect of the extra scan that will subsequently be
performed.
sinclude
Similar to include, except it ignores any errors.
spaste
Similar to paste, except it ignores any errors.
substr
Returns a substring of the first argument, starting at the
offset specified by the second argument and the length specified by
the third argument. If no third argument is present, it returns the
rest of the string.
syscmd
Passes the first argument to the shell. Nothing is
returned.
sysval
Returns the return value from the last syscmd.
translit
Transliterate the characters in the first argument from the set
given by the second argument to the set given by the third. You
cannot use tr(1)-style abbreviations.
undefine
Removes the definition for the macro specified by the first
argument.
undivert
Flushes the named output queues (or all queues if there are no
arguments).
unix
A pre-defined macro for testing the operating system
platform.