m4(1)

NAME
m4 - macro language processor

SYNOPSIS
m4 [ -Dname[=value]] [-Uname]

DESCRIPTION
The m4 utility is a macro processor that can be used as a front end to any language (e.g., C, ratfor, fortran, lex, and yacc). m4 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 parenthesis '('. If the macro name is not followed by an open parenthesis it is processed with no arguments.

Macro names consist of a leading alphabetic or underscore possibly followed by alphanumeric or underscore characters, therefore 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 (e.g., ` 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[
    =value] Define the symbol name to have some value (or NULL).

-Uname
    Undefine the symbol name.

SYNTAX
m4 provides the following built-in macros. They may 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 may 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 n'th argument. $0 is the name of the calling macro. 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 10 output queues (numbered 0-9). At the end of processing m4 concatenates all the queues in numerical order to produce the final output. Initially the output queue is 0. The divert macro allows you 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 any) specifies the radix for the result and the third argument (if any) 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 then 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 then 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 arguments 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 (e.g., 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.

m4wrap
    Allows you to define what happens at the final EOF, usually for cleanup purposes (e.g., 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 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 pushdef'ed definition for each argument.

pushdef
    Takes the same arguments as define, but it 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 in between. 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 no arguments).

unix
    A pre-defined macro for testing the OS platform.

AUTHOR
Ozan Yigit <oz@sis.yorku.ca> and Richard A. O'Keefe (ok@cs.rmit.edu.au)