What tools are there for debugging/stepping through a regular expression?
While there are many good online and offline tools for testing regular expressions, I have yet to find a tool (besides RegexBuddy) that lets me see the steps that the regular expression engine takes to find a match (or to find that there is no match, for that matter.)
Does anyone know of any tools that do this? The reason I have initially excluded RegexBuddy is because it's commercial and I would prefer to look over my options before I decide to pay for it.
To make it clearer what I want, here is a screenshot from RegexBuddy (from their home page): http://img166.imageshack.us/img166/1272/debug.png
Perhaps RegexCoach offers what you're looking for...
http://weitz.de/regex-coach/
In Perl you can always just use re 'debug'; or use re 'debugcolor';
For example if you enter this into Perl:
use strict;
use warnings;
use 5.010;
use re 'debug';
# using the same strings as the question's image for reference:
my $str = 'Even if I do say so myself: "RegexBuddy is awesome"';
$str =~ /(Regexp?Buddy is (awful|acceptable|awesome))/;
This is what you get out:
Compiling REx "(Regexp?Buddy is (awful|acceptable|awesome))"
Final program:
1: OPEN1 (3)
3: EXACT <Regex> (6)
6: CURLY {0,1} (10)
8: EXACT <p> (0)
10: EXACT <Buddy is > (14)
14: OPEN2 (16)
16: EXACT <a> (18)
18: TRIEC-EXACT[cw] (29) # this is a new feature in Perl 5.10
<wful>
<cceptable>
<wesome>
29: CLOSE2 (31)
31: CLOSE1 (33)
33: END (0)
anchored "Regex" at 0 floating "Buddy is a" at 5..6 (checking floating) minlen 19
Guessing start of match in sv for REx "(Regexp?Buddy is (awful|acceptable|awesome))" against 'Even if I do say so myself: "RegexBuddy is awesome"'
Found floating substr "Buddy is a" at offset 34...
Found anchored substr "Regex" at offset 29...
Starting position does not contradict # /^/m...
Guessed: match at offset 29
Matching REx "(Regexp?Buddy is (awful|acceptable|awesome))" against 'RegexBuddy is awesome"'
29 <'lf: "'> <RegexBuddy> | 1:OPEN1(3)
29 <'lf: "'> <RegexBuddy> | 3:EXACT <Regex>(6)
34 <Regex> <Buddy is a> | 6:CURLY {0,1}(10)
EXACT <p> can match 0 times out of 1...
34 <Regex> <Buddy is a> | 10: EXACT <Buddy is >(14)
43 <y is > <'awesome"'> | 14: OPEN2(16)
43 <y is > <'awesome"'> | 16: EXACT <a>(18)
44 < is a> <'wesome"'> | 18: TRIEC-EXACT[cw](29)
44 < is a> <'wesome"'> | State: 2 Accepted: 0 Charid: 2 CP: 77 After State: 3
45 < is aw> <'esome"'> | State: 3 Accepted: 0 Charid: 7 CP: 65 After State: 10
46 < is awe> <'some"'> | State: 10 Accepted: 0 Charid: b CP: 73 After State: 11
47 < is awes> <'ome"'> | State: 11 Accepted: 0 Charid: c CP: 6f After State: 12
48 < is aweso> <'me"'> | State: 12 Accepted: 0 Charid: d CP: 6d After State: 13
49 < is awesom> <'e"'> | State: 13 Accepted: 0 Charid: 7 CP: 65 After State: 14
50 < is awesome> <'"'> | State: 14 Accepted: 1 Charid: 3 CP: 0 After State: 0
got 1 possible matches
only one match left: #3 <wesome>
50 < is awesome> <'"'> | 29: CLOSE2(31)
50 < is awesome> <'"'> | 31: CLOSE1(33)
50 < is awesome> <'"'> | 33: END(0)
Match successful!
Freeing REx: "(Regexp?Buddy is (awful|acceptable|awesome))"
( Note: I changed some parts of the output, so that it would highlight better )
It's not quite as powerful as RegexBuddy, but it's a simple online interface: http://www.gskinner.com/RegExr/
You can mouse-over parts of your expression and it will tell you what it's doing. Very basic, but it can really save time when you do something stupid.
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