Regex keeps looping on itself :/

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

Hi, I'm trying to write a bit of regex, which will got through a list of tags like [something] , and convert to their correct article_id (kinda like a wiki) The code I have is:

 # for tags like [[something]]
  while ($post_message =~ m%\[\[([^]]+)\]\]%gix) {

    if ($1 =~ /\|/) { next; }

    my $tmp = $1;
    my $val = $1;

#    print STDERR "\n\nFOO\n\n";

    if ($DB->table('Articles')->count( { article_title => $tmp } ) > 0
+) {
         print TESTOUT "\n\nFOO 2 - gggg - $tmp \n\n";
        my $article_id = $DB->table('Articles')->select( ['article_id'
+], { article_title => $tmp } )->fetchrow;
        $tmp =~ tr{&[]ÀÂÄàâäÇçÉÊÈËéêèëÏÌÎïìîÖÔÒöôòÜÛÙüûùA-Z?!;«»()" }{
+   aaaaaacceeeeeeeeiiiiiioooooouuuuuua-z         _};
          $tmp =~ s/ /_/g;
        $post_message =~ s/\Q[[$1]]/[[$article_id]]/sig;
    } else {

    ` # do something here latest

    }

  }
[download]

..but it keeps on looping over and over the same stuff (untl the script dies, or I kill the process in SSH) An example post is:

==Introduction==

A Montréal, il y a [[vieux Montréal]].

[[Montréal]]

[[test]]

==Brief History==
asdfasfd
as
df
asf
d
asdf
as
fd
asf
dasfd
==Geography==
==Regions==
==Cities==
==Sights and Activites==
==Weather==
==Getting There==
==END Getting There==
[download]

Can anyone suggest why it keeps doing this kinda stuff: FOO 2 - gggg - vieux Montréal FOO 2 - gggg - Montréal FOO 2 - gggg - vieux Montréal FOO 2 - gggg - 45 FOO 2 - gggg - vieux Montréal FOO 2 - gggg - 47 FOO 2 - gggg - vieux Montréal FOO 2 - gggg - 48 FOO 2 - gggg - vieux Montréal TIA! Andy

Comment on Regex keeps looping on itself :/ Select or Download Code

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Re: Regex keeps looping on itself :/ by moritz (Cardinal) on Jun 17, 2009 at 15:44 UTC
`$str =~ m/.../g` in scalar context keeps track of its current position via `pos($str)`, and `$str =~ s/.../.../g` resets `pos($str)`. You could something along these lines instead: `$post_message =~ s{\[\[([^]]+)\]\]}{process_match($1)}ge; sub process_match { my $tmp = shift; if ($DB->table('Articles')->count( { article_title => $tmp } ) > 0) + { # return modified text here } else { return $tmp; # unmodified text } }` [download]	[reply] [d/l] [select]
Re^2: Regex keeps looping on itself :/ by ultranerds (Hermit) on Jun 18, 2009 at 14:41 UTC
Hi, The solution works perfectly - thank you very much :) Will have to remember that trick for another time. Cheers Andy	[reply]
Re: Regex keeps looping on itself :/ by ikegami (Patriarch) on Jun 17, 2009 at 15:35 UTC
The following expression resets the position at which the next match will start: `$post_message =~ s/\Q[[$1]]/[[$article_id]]/sig;` [download] You'd be better off reading from one var and storing the output in another. `while ($input =~ /\G(.?)\[\[([^]]+)\]\]/sg) { my $link = $2; $output .= $1; $output .= process($link); }` [download] Update*: Oops, there's a bug in the above. It drops whatever's after the last link. It's actually easier to solve using a different technique. `$post_message =~ s{\[\[([^]]+)\]\]}{ process($1) }esg;` [download]	[reply] [d/l] [select]
Re^2: Regex keeps looping on itself :/ by ultranerds (Hermit) on Jun 17, 2009 at 15:43 UTC
Thanks - that never gets any values though :/ `my $post_message = $DB->table('Post')->select( ['post_message'], { p +ost_id => $_[0] } )->fetchrow; print TESTOUT qq\|testing the output of post_message - $post_message +\n\n \|; $post_message =~ s{\[\[([^]]+)\]\]}{ # process($1) print TESTOUT qq\|FOO: "$1"\|; }esg` [download] TIA Andy	[reply] [d/l]
Re^3: Regex keeps looping on itself :/ by ikegami (Patriarch) on Jun 17, 2009 at 15:53 UTC
It gets replaced with the result of the expression. In this case, it gets replaced with 1, the result of `print`. Remove `print TESTOUT`	[reply] [d/l] [select]