in reply to Reverse regexp a regexp?

I am also not sure what you exactly want to achieve by your second question, however try this: 
#! /usr/bin/perl

use strict;
use warnings;
use Regexp::Assemble;

my @urls = qw(
  http://www.youtube.com/user/test1
  http://www.youtube.com/user/test2
  http://www.youtube.com/user/test3
  http://www.youtube.com/user/test4
  http://www.youtube.com/user/test5 );
my $r = Regexp::Assemble->new;

for (@urls) {
  $r->add( quotemeta );
}

print $r->re, $/;

__END__

[download]
output: (?-xism:http:\/\/www\.youtube\.com\/user\/test[12345])

And you may also find valuable the String-Approx distribution from CPAN which implements approximate string matching based on Levenshtein distance.

Hope this helps.

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Re^2: Reverse regexp a regexp?
by freakingwildchild (Scribe) on Feb 13, 2010 at 23:09 UTC
    Very interesting approach of assembling regexes; although this would not generate the results required when inputting real life data like:

    my @urls = qw(
  http://www.youtube.com/user/jantje
  http://www.youtube.com/user/pieter
  http://www.youtube.com/user/frida
  http://youtube.com/user/channel
  http://youtube.com/channel/doesntexist
  http://youtube.com/user/blah
  http://www.youtube.com/user/bianca_sterlings
  http://www.youtube.com/user/blango );

    [download]

    Which returns: 

    (?-xism:http:\/\/(?:www\.youtube\.com\/user\/(?:b(?:ianca_sterlings|la
+ngo)|jantje|pieter|frida)|youtube\.com\/(?:user\/(?:channel|blah)|cha
+nnel\/doesntexist)))

    [download]

    while it should return roughly: ^http:\/\/(?:www\.)youtube\.com\/user\/(.*)$

    What this module offers is a rather customized approach of how to create regexes on custom user data, for validation; while I'd like to create a regex on public data to extract the right set of data out of a list of url's. Thanks for letting me know this this one; it's a nice toy to play with :D

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