yoda54 has asked for the wisdom of the Perl Monks concerning the following question:

Monks,

I don't understand why my $3 includes the slash and everything after and not just "to"?

Thanks for any advice!


#!/usr/bin/perl
use strict;
use warnings;

$a = "some/path/to/somewhere/hello";
if ($a =~ /(.+)(\/path\/)(.+)(\/.+)/)
{
   print "$1 -> $3\n";
}

Output:

some -> to/somewhere

[download]

Replies are listed 'Best First'.
Re: Regex help
by GrandFather (Saint) on Sep 10, 2012 at 04:00 UTC

    + is greedy and will match as many of whatever it applies to as it can. Generally it is smart to avoid . and use an explicit set of characters to match. In this case everything except / looks like it may be what you want:

    $str =~ m!(.+)(/path/)([^/]+)(/.+)!

    [download]

    Note that I used ! as the regex delimiter to avoid having to quote all the / characters.

    True laziness is hard work
[reply]
[d/l]
      Thank you sir! :-D
[reply]
Re: Regex help
by Anonymous Monk on Sep 10, 2012 at 03:58 UTC
    Because it does :) Add 
    use re 'debug';

    [download]
    and watch the regex engine match the thing

    Also see 

    use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new(
    qr/(.+)(\/path\/)(.+)(\/.+)/
)->explain;
__END__
The regular expression:

(?-imsx:(.+)(/path/)(.+)(/.+))

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):
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    .+                       any character except \n (1 or more times
                             (matching the most amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  (                        group and capture to \2:
----------------------------------------------------------------------
    /path/                   '/path/'
----------------------------------------------------------------------
  )                        end of \2
----------------------------------------------------------------------
  (                        group and capture to \3:
----------------------------------------------------------------------
    .+                       any character except \n (1 or more times
                             (matching the most amount possible))
----------------------------------------------------------------------
  )                        end of \3
----------------------------------------------------------------------
  (                        group and capture to \4:
----------------------------------------------------------------------
    /                        '/'
----------------------------------------------------------------------
    .+                       any character except \n (1 or more times
                             (matching the most amount possible))
----------------------------------------------------------------------
  )                        end of \4
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

    [download]
[reply]
[d/l]
[select]
      Thanks!
[reply]

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