Stumped Regular expressions

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

Dear monks, I'm trying to match all instances of "http://hosting/image1.jpg http://hosting/image1.jpg http://hosting/image4.jpg" in a single string but I can't seem to get this to work? Any advice? Thanks!

#!/usr/bin/perl

use strict;
use warnings;


open(F, "test.htm");

while(<F>) {
   my @a = ($_ =~ /(http:\/\/hosting.+\.rar)/g );
   foreach(@a) { 
      chomp;
      print "$_\n"; 
   }
}

close(F);
[download]

Comment on Stumped Regular expressions Download Code

Replies are listed 'Best First'.
Re: Stumped Regular expressions by moritz (Cardinal) on Jun 10, 2008 at 10:11 UTC
If the URLs have the structure you described above, they will not match `\.rar`. If you have slashes in the regex, chose a different delimiter to avoid the backslashes: `m{(http://hosting/image\d+\.jpg)}` If you are looking for URLs in general, consider Regexp::Common::URI.	[reply] [d/l] [select]
Re: Stumped Regular expressions by psini (Deacon) on Jun 10, 2008 at 10:31 UTC
Moreover, your .+ is greedy, so your regex will match only (at most) one substring in the string, starting with the first http://hosting and ending with the last .rar. If you want to individually catch all the occurrences, you should use a non greedy modifier (ie .+?) Careful with that hash Eugene.	[reply]
Re: Stumped Regular expressions by Grey Fox (Chaplain) on Jun 10, 2008 at 20:28 UTC
I have found http://www.regular-expressions.info/quickstart.html very helpful working with regex's. Lots of good examples. -- Grey Fox "We are grey. We stand between the darkness and the light" B5	[reply]
Re: Stumped Regular expressions by kabeldag (Hermit) on Jun 11, 2008 at 13:48 UTC
I stuck a 'global' modifier on the end: `use strict; use warnings; my $line_count = 0; open(F, "test.htm"); while(<F>) { my @a = $_ =~ m{(http://hosting/image\d+\.jpg)}g; for my $url (@a) { print "URL [ $url ] found on line ($line_count)\n"; } $line_count++; } close(F);` [download]	[reply] [d/l]
Re^2: Stumped Regular expressions by toolic (Bishop) on Jun 11, 2008 at 16:34 UTC
This could be further simplified by using the special variable `$.` (INPUT_LINE_NUMBER) instead of `$line_count`: `open(F, "test.htm"); while(<F>) { my @a = $_ =~ m{(http://hosting/image\d+\.jpg)}g; for my $url (@a) { print "URL [ $url ] found on line ($.)\n"; } } close(F);` [download]	[reply] [d/l] [select]


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