Tip #9 from the Basic debugging checklist:

Demystify regular expressions by installing and using the CPAN module YAPE::Regex::Explain

So:

#! perl
use strict;
use warnings;
use YAPE::Regex::Explain;

my $re = qr/(?<=module )$ARGV[2].*?([\\(;])/;

print YAPE::Regex::Explain->new($re)->explain();

[download]

Output:

15:40 >perl 566_SoPW.pl FILE OLD NEW
The regular expression:

(?-imsx:(?<=module )NEW.*?([\\(;]))

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  (?<=                     look behind to see if there is:
----------------------------------------------------------------------
    module                   'module '
----------------------------------------------------------------------
  )                        end of look-behind
----------------------------------------------------------------------
  NEW                      'NEW'
----------------------------------------------------------------------
  .*?                      any character except \n (0 or more times
                           (matching the least amount possible))
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    [\\(;]                   any character of: '\\', '(', ';'
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

15:40 >

[download]

See also perlretut and perlre.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

In reply to Re^3: Bug in script, regex help req extreme urgent by Athanasius
in thread Bug in script, regex help req extreme urgent by sid.verycool

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