RegEx question

erabus has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I am hoping to get some help with a RegEx.

The first block does not match but the second block does. The difference is that the second block has the pipe character after “greg herman”. It wasn’t obvious to me why the last match string needed a pipe before the closing parenthesis. Any ideas?

Thanks. -Tony

#!/usr/bin/perl -w
require 5.010_000;
use strict;
use warnings;
use feature ':5.10';

my $name='tom jones';

{
    my $gender;
    
    given ( $name )
    {
        when ( /^
                    (
                        tom jones|
                        greg herman
                    )
                /xms
             )
        {
            $gender='male';
        }
    }
    say 'gender='.( $gender//'undef' );
}

{
    my $gender;
    
    given ( $name )
    {
        when ( /^
                    (
                        tom jones|
                        greg herman|
                    )
                /xms
             )
        {
            $gender='male';
        }
    }
    say 'gender='.( $gender//'undef' );
}

exit;
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Comment on RegEx question Download Code

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Re: RegEx question by crashtest (Curate) on Feb 04, 2010 at 01:04 UTC
The pipe in the second block turned your regex into one that will match any string, including `Joe Blow`, `Amelia Earhardt` and `Barack Obama`. With the trailing pipe, your code now says: Match tom jones, or greg herman, or... whatever. So whatever matches. The problem with the regex in the first block is that you're using the `x` modifier, something you appear to have forgotten when you wrote `tom jones` and `greg herman`. Note the space in between the first and last names - Perl is ignoring it. That regex will in fact match the string `tomjones` and `gregherman`. To make it work the way you want it to, you have to say `tom\sjones \| greg\sherman`. Hope this helps!	[reply] [d/l] [select]
Re^2: RegEx question by erabus (Sexton) on Feb 04, 2010 at 01:32 UTC
Thank you.	[reply]