Regular Expression Debugger ?

[John M. Dlugosz]

I know I've seen discussion of such a beast, but Super Search on the title phrase didn't find anything. Anybody know?

A friend of mine is interested in learning R.E. and I remembered hearing about that.

—John

[Ovid]

Try this snippet:

#!/usr/bin/perl -w
use strict;

use re 'debug';
my $test = "abc123abc1234abc";

$test =~ /(\d{4})/;
print $1;

The output from that is:

Compiling REx `(\d{4})'
size 8 first at 5
   1: OPEN1(3)
   3:   CURLY {4,4}(6)
   5:     DIGIT(0)
   6: CLOSE1(8)
   8: END(0)
stclass `DIGIT' minlen 4
Matching REx `(\d{4})' against `abc123abc1234abc'
  Setting an EVAL scope, savestack=5
   3 <abc> <123abc123>    |  1:  OPEN1
   3 <abc> <123abc123>    |  3:  CURLY {4,4}
                           DIGIT can match 3 times out of 4...
  Setting an EVAL scope, savestack=5
                            failed...
  Setting an EVAL scope, savestack=5
   4 <abc1> <23abc123>    |  1:  OPEN1
   4 <abc1> <23abc123>    |  3:  CURLY {4,4}
                           DIGIT can match 2 times out of 4...
  Setting an EVAL scope, savestack=5
                            failed...
  Setting an EVAL scope, savestack=5
   5 <abc12> <3abc123>    |  1:  OPEN1
   5 <abc12> <3abc123>    |  3:  CURLY {4,4}
                           DIGIT can match 1 times out of 4...
  Setting an EVAL scope, savestack=5
                            failed...
  Setting an EVAL scope, savestack=5
   9 <23abc> <1234abc>    |  1:  OPEN1
   9 <23abc> <1234abc>    |  3:  CURLY {4,4}
                           DIGIT can match 4 times out of 4...
  Setting an EVAL scope, savestack=5
  13 <23abc1234> <abc>    |  6:    CLOSE1
  13 <23abc1234> <abc>    |  8:    END
Match successful!
1234Freeing REx: `(\d{4})'

It's fairly complicated, but if you really need to get into the guts of how regular expressions work, that should do it.

Cheers,
Ovid

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[LD2]

Check out this node: Rebug Back Online.

[RhetTbull]

While not really a debugger, I'm partial to japhy's excellent YAPE::Regex::Explain which does a great job explaining regex's in plain English.

-RT

[Fletch]

There's also Dominus' Rx

[dvergin]

The Komodo programming environment from ActiveState includes a very interesting dynamic regex debugging feature. You can do things like: tweak the regex and the highlighting in your test strings changes to show what will be matched, etc.

[davorg]

Which is based on Rx. Dominus wrote an excellent paper on the development of Rx. It won a "best paper" award at The Perl Conference this year. It's included in the proceedings of the conference or on his web site.

--
<http://www.dave.org.uk>

"The first rule of Perl club is you don't talk about Perl club."