NAME

SYNOPSIS

    my $foo = Regexp::Log::Foo->new(
        format  => 'custom %a %b %c/%d',
        capture => [qw( host code )],
    );

    # the format() and capture() methods can be used to set or get
    $foo->format('custom %g %e %a %w/%s %c');
    $foo->capture(qw( host code ));

    # this is necessary to know in which order
    # we will receive the captured fields from the regexp
    my @fields = $foo->capture;

    # the all-powerful capturing regexp :-)
    my $re = $foo->regexp;

    while (<>) {
        my %data;
        @data{@fields} = /$re/;    # no need for /o, it's a compiled regexp

        # now munge the fields
        ...
    }

DESCRIPTION

The goal of this module family is to compute regular expressions based on the configuration string of the log.

Please note that there is nothing useful you can do with Regexp::Log! Use one of its derived classes!

METHODS

Please note that all the accessors return the new value, if used to set.

new( %args )

Return a new Regexp::Log object. A list of key-value pairs can be given to initialise the object.

The default arguments are:

 format      - the format of the log line
 capture     - the name of the fields to capture with the regexp
               (given as an array ref)
 comments    - leave the (?#=name) ... (?#!name) comments in the regexp
 anchor_line - include begin (^) and end ($) anchor in the regexp
 modifiers   - include the modifiers into regexp
    

Other arguments (and the corresponding accessors) can be defined in derived classes.

format( $formatstring )

This accessor sets or gets the format string used as a template to generate the log-matching regexp. This is usually the configuration line of the log-generating software.

capture( @fields )

Add the elements of @fields to the list of fields that the regular expression should capture (if possible).

The method returns the list of actually captured fields, in the same order as the regular expression captures.

The special tags ":none" and ":all" can be used to capture none or all of the fields. ":none" can also be used to reset a capture list, as shown in the following example:

    my $log = Regexp::Log::Foo->new( format => $format );

    # create a regexp that will capture gmttime and host
    $log->capture(qw( gmttime host ));
    my $re1 = $log->regexp;    # captures gmttime and host

    # add username to the list of captured fields
    $log->capture(qw( username ));
    my $re2 = $log->regexp;    # captures gmttime, host and username

    # start afresh and capture username and uri
    $log->capture(qw( :none username uri ));
    my $re3 = $log->regexp;    # captures username and uri
    

When used to set, this method returns the new list of captured fields, in capture order.

regexp( )

Return a computed regular expression, computed from the data given to the Regexp::Log object, and ready to be used in a script.

regex( )

regex() is an alias for the regexp() method.

fields( )

This method return the list of all the fields that can be captured.

For complex subclasses making a lot of modifications in _preprocess() and _postprocess(), the result may not be accurate.

The result of fields() is therefore given for information only.

comments( $bool )

Accessor for the "comments" attribute.

Comments are removed by default.

modifiers( $modifiers )

Sets the modifiers that govern how the pattern behaves (for versions of Perl up to 5.9 or so, these are "imsx"). By default no flags are enabled.

anchor_line( $bool )

The resulting pattern will be have the "^" and "$" line boundary assertions at the beginning and end of the pattern, respectively, when the value is true. Set to 0 to disable.

debug( $bool );

Get/set regexp debug mode.

If "debug" is set, each time a field (or subfield) is matched, its name (followed by a space) is printed on STDERR. A newline is printed at the beginning of the search. This lets you see where the regexp backtracks, and watch all its attempts to match something. Useful but usually very verbose.

This is mainly useful when writing a new Regexp::Log subclass.

SUBCLASSES

    package Regexp::Log::Foo;

    use base qw( Regexp::Log );
    use vars qw( $VERSION %DEFAULT %FORMAT %REGEXP );

    $VERSION = 0.01;

    # default values
    %DEFAULT = (
        format  => '%d %c %b',
        capture => [ 'c' ],
    );

    # predefined format strings
    %FORMAT = ( ':default' => '%a %b %c', );

    # the regexps that match the various fields
    # this is the difficult part
    %REGEXP = (
        '%a' => '(?#=a)\d+(?#!a)',
        '%b' => '(?#=b)th(?:is|at)(?#!b)',
        '%c' => '(?#=c)(?#=cs)\w+(?#!cs)/(?#=cn)\d+(?#!cn)(?#!c)',
        '%d' => '(?#=d)(?:foo|bar|baz)(?#!d)',
    );

    # Note that the three hashes (%DEFAULT, %FORMAT and %REGEXP)
    # MUST be defined, even if they are empty.

    # the _regexp field is an internal field used as a template
    # by the regexp()

    # the _preprocess method is used to modify the format string
    # before the fields are expanded to their regexp value
    sub _preprocess {
        my $self = shift;

        # multiple consecutive spaces in the format are compressed
        # to a single space
        $self->{_regexp} =~ s/ +/ /g;
    }

    # the _postprocess method is used to modify the format string
    # after the fields are expanded to their regexp value

    1;

    my $log = Regexp::Log::Foo->new(
        format => ':default',
        capture => [ qw( c cn ) ],
    );
    my $re = $log->regexp;
    my @fields = $log->capture();

    while(<>) {
        my @data;
        @data{@fields} = (/$re/g);

        # some more code
    }

    $Regexp::Log::Foo::REGEXP{'%d'} = '(?#=d)(?:fu|foo|bar|baz)(?#!d)'

BUGS

The t/20debug.t test file fails with Perl 5.6.0 and 5.6.1. I have no idea why, but it may be linked to the use of the "(?{ ... })" regexp construct in the debugging code.

AUTHOR

LICENCE