Filter::m4

Section: User Contributed Perl Documentation (3)
Updated: 2021-01-27
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NAME

Filter::m4 - M4 source filter

SYNOPSIS

    use Filter::m4;
    use Filter::m4 'prefix';

DESCRIPTION

This source filter pipes the current source file through the M4 macro processor ("m4") if it is available.

As with all source filters its scope is limited to the current source file only. Every file you want to be processed by the filter must have the following line near the top.

    use Filter::m4;

EXAMPLE

Here is a small example that shows how to define and use an M4 macro:

    use Filter::m4;

    define(`foo', `$1 =~ s/bar/baz/r')

    $a = "foobar";
    print "a = " . foo(`$a') . "\n";

The output of the above example:

    a = foobaz

NOTES

By default, M4 uses ` and ' as quotes; however, this is configurable using M4's "changequote" builtin.

M4 uses $1, $2, etc., to indicate arguments in macros. To avoid clashes with Perl regex syntax it is recommended to use Perl's alternative forms "${1}", "${1}", etc.

The following keywords in M4 and Perl are identical:

    eval
    format
    index
    mkstemp
    shift
    substr

If you need such keywords in your Perl code you have to use one of the following three solutions.

•: Protect the keyword with M4 quotes, for example `shift'.
•: Redefine the problematic M4 builtin using "defn", as outlined in section Renaming macros of the M4 info manual.
•: Use the "prefix" option. This adds the prefix "m4_" to all M4 builtins (but not to user-defined macros). For example, you will have to use "m4_shift" instead of "shift".

AUTHOR

Werner Lemberg

DATE

17th March 2018.