in reply to Reading Reg Exp

You could also try YAPE::Regex::Explain. Thanks to Toolic for suggesting this module in a previous post. Here is an example using one of your regexes:

#!perl
use strict;
use warnings;

use YAPE::Regex::Explain;

print YAPE::Regex::Explain->new(qr/(?:\w+\s+fish\s+){2}(\w+)\s+fish/i)
+->explain();

__END__
The regular expression:

(?i-msx:(?:\w+\s+fish\s+){2}(\w+)\s+fish)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?i-msx:                 group, but do not capture (case-insensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  (?:                      group, but do not capture (2 times):
----------------------------------------------------------------------
    \w+                      word characters (a-z, A-Z, 0-9, _) (1 or
                             more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    \s+                      whitespace (\n, \r, \t, \f, and " ") (1
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
    fish                     'fish'
----------------------------------------------------------------------
    \s+                      whitespace (\n, \r, \t, \f, and " ") (1
                             or more times (matching the most amount
                             possible))
----------------------------------------------------------------------
  ){2}                     end of grouping
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \w+                      word characters (a-z, A-Z, 0-9, _) (1 or
                             more times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  \s+                      whitespace (\n, \r, \t, \f, and " ") (1 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  fish                     'fish'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

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Update: Link fixed.

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Re^2: Reading Reg Exp
by JavaFan (Canon) on Aug 11, 2010 at 09:11 UTC 
    \s+                      whitespace (\n, \r, \t, \f, and " ")
    That's actually incorrect. \s matches 25 different characters, although locale (and EBCDIC) can change the set of characters matched. Even in the LATIN-1 range, next line ("\x85") and no-break space ("\xA0") will be matched by \s if either the pattern or subject has the UTF-8 flag set.
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[select]

      YAPE::Regex::Explain is probably only set up for the most common uses; since it uses YAPE::Regex to parse the regex, it probably can't detect encoding or locale. Since it is only providing an explanation of the regex, in most cases it wouldn't really matter.

[reply]
        But even ignoring locale or encoding, it's still not listing 80% of the characters the class can match. That's like saying [a-z] matches all the vowels.
[reply]
[d/l]

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