I know that, in the past, I've just wanted to jam something into $1 - it seems a natural way of expressing what I want to do. Unfortunately Perl doesn't do it this way. So you've got to think of other means. And there are many approaches (see perlre).

One method might be to calculate where the match of your capture finishes, calculate where the capture started, and replace that portion of the string directly using substr.

Example code:

use strict;

my $val =
    'http://adserver.adtech.de/'
    . '?addyn|2.0|323|91793|1|277|target=_blank';

my $re = qr/
    .*\|.*\|.*\|.*\|.*\|
    (.*)
    (?=\|.*) # look-ahead
/x;

if ( $val =~ m/$re/g ) {
    print( "found: \"$1\"\n" );
    print( "pos is: " . scalar( pos( $val ) ) . "\n" );
    print( "behind pos is: \"" .
        substr( $val, pos( $val ) - length( $1 ), length( $1 ) )
        . "\"\n"
    );

    # perform substitution here using calculated offsets
    substr( $val, pos( $val ) - length( $1 ), length( $1 ) ) = "moo";
    print( "$val\n" );
}

[download]

The problem is that you have to use a look-ahead to prevent the pos function returning the end of the entire regexp match.. The other problem is that you have to use the /g (global) flag on your match to ensure the position is calculated.

This code replaces the "277" with the word "moo". Try it!

In reply to Re: Replace part of a regex match by monarch
in thread Replace part of a regex match by krisravn

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