January 26, 1993 M4 1

### NAME

m4 - macro language processor

### SYNOPSIS

m4 [-Pg] [-Dname[=value]] [-I dirname] [-Uname] [-d flags] [-o trfile] [-t name]

### 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, e.g., valid macro names match the pattern ``[a-zA-Z_][a-zA-Z0-9_]*''.

In arguments to macros, leading unquoted space, tab, and newline (`\n') 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.

Most built-ins don't make any sense without arguments, and hence are not recognized as special when not followed by an open parenthesis.

The options are as follows:

=value [

-Dname
  ] Define the symbol name to have some value (or ```NULL`).

-I dirname
  Add directory dirname to the include path.

-P
  Prefixes all m4 builtin macros with the string ``m4_''. This changes the macro names ``dnl'' to ``m4_dnl'', ``index'' to ``m4_index'', and so forth.

-Uname
  Undefine the symbol name.

-d flags
  Set trace flags. flags may hold the following:

  a
    print macro arguments.

  c
    print macro expansion over several lines.

  e
    print result of macro expansion.

  f
    print filename location.

  l
    print line number.

  q
    quote arguments and expansion with the current quotes.

  t
    start with all macros traced.

  x
    number macro expansions.

  V
    turn on all options.

  By default, trace is set to "eq.

-g
  Activate GNU-m4 compatibility mode. In this mode, changequote with two empty parameters deactivates quotes, translit handles simple character ranges (e.g., a-z), regular expressions mimic emacs behavior, and the number of diversions is unlimited.

-o trfile
  Specify the tracing output file for -t; tracing defaults to printing to stderr.

-t macro
  Turn tracing on for macro.

### SYNTAX

m4 provides the following built-in macros. They may be redefined, losing their original meaning. Return values are null unless otherwise stated.

builtin
  Calls a built-in by its name, overriding possible redefinitions.

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.

esyscmd
  Pass its first argument to a shell and returns the shell's standard output. Note that the shell shares its standard input and standard error with .

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. If the file is not found as is, look through the include path: first the directories specified with -I on the command line, then the environment variable ```M4PATH`, as a colon-separated list of directories. 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.

indir
  Indirectly calls the macro whose name is passed as the first arguments, with the remaining arguments passed as first, ... arguments.

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 be 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.

patsubst
  Substitutes a regular expression in a string with a replacement string. Usual substitution patterns apply: an ampersand (`&') is replaced by the string matching the regular expression. The string ``\#'', where `#' is a digit, is replaced by the corresponding back-reference.

popdef
  Restores the pushdefed definition for each argument.

pushdef
  Takes the same arguments as define, but it saves the definition on a stack for later retrieval by popdef.

regexp
  Finds a regular expression in a string. If no further arguments are given, it returns the first match position or -1 if no match. If a third argument is provided, it returns the replacement string, with sub-patterns replaced.

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.

traceon
  Enables tracing of macro expansions for the given arguments, or for all macros if no argument is given.

traceoff
  Disables tracing of macro expansions for the given arguments, or for all macros if no argument is given.

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.

__line__
  Returns the current file's line number.

__file__
  Returns the current file's name.

### STANDARDS

The m4 utility is expected to be a superset of the X/Open Commands and Utilities Issue 5 (``XCU5'') specification, and includes some extensions also present in GNU .

The -s option #line directives (cpp(1)'s) is currently not supported. Flags -I, -d, -t are non-standard.

The output format of tracing and of dumpdef are not specified in any standard, are likely to change and should not be relied upon. The current format of tracing is closely modelled on GNU , to allow autoconf to work.

For portability, one should not use the macros builtin, esycmd, expr, indir, paste, patsubst, regexp, spaste, unix, __line__, __file__.

All builtins do expand without arguments in many other .

### AUTHORS

Ozan Yigit <oz@sis.yorku.ca> and Richard A. O'Keefe (ok@cs.rmit.edu.au). GNU-m4 compatibility extensions by Marc Espie <espie@cvs.openbsd.org>.