The problem with either method is that there are special cases which one might miss unless they understand exactly what a URL might look like (or for that case any data you have to parse through).

Personally, I would use a module if someone has already taken the time to do the leg work of what specifications an URL has to meet.

When I initially coded up a regex for this, and then didn't post it because I don't wish to do someone elses homework, but rather posted the method I took, and I completely neglected the special case that fruiture mentions above. But I don't see a problem with using split(s). Anyhow, on to the code (granted no guarantees that it will work for all cases, I would use URI):

use strict;
use warnings;

while ( my $url = <DATA> )
{
  chomp($url);
  my $dup_url = $url;

  if ( length($url) > 49)
  {
  $url =~ s!(?:
              (^https?://[^/]+/).*/(.*)\?.*
            )
            |
            (?:
               (^https?://[^/]+/).*/(.*)
            )
           !
           ($1||$3) . '(...)/'. ($2||$4)
           !ex;

   my $http = (split /\/\//,$dup_url)[0];
   my ($url_start, $url_end) = (split /\//  ,(split /\?/,$dup_url)[0])
+[2,-1];
   $dup_url = "$http//$url_start/(...)/$url_end";

  }

  print "REGEX: $url\n";
  print "SPLIT: $dup_url\n\n";

}

__DATA__
http://some-shop.com/dir1/dir2/buystuff.cgi?x=1&y=2&z=3
http://somewhere/with/a/vastly/deep/structure/virus.exe
http://host.com/some/uri/whatever?some/query/stringthatis/here
https://some-shop.com/dir1/dir2/buystuff.cgi?x=1&y=2&z=3
https://somewhere/with/a/vastly/deep/structure/virus.exe
https://host.com/some/uri/whatever?some/query/stringthatis/here
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