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

I'm trying to use a regex to get the filename of this URL: http://txs.corp.com:8080/area/es/2215.csv.gz

Why isn't this doing a non-greedy match and getting "2215.csv.gz" in the scalar $gzip?

I know I can use a module for this, but I'm trying to figure out what's wrong with my regex knowledge. 
    my $file = 'http://txs.corp.com:8080/area/es/2215.csv.gz';
    my ( $gzip ) = $file =~ m/\/(.*?\.gz)$/;

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Replies are listed 'Best First'.
Re: Why is this greedy matching?
by toolic (Bishop) on Mar 23, 2012 at 14:41 UTC
    File::Basename is easier: 
    use warnings;
use strict;
use File::Basename;

my $file = 'http://txs.corp.com:8080/area/es/2215.csv.gz';
my $gzip = basename($file, qr/\.gz/);
print "$gzip\n";

__END__

2215.csv.gz

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    Demystify regular expressions by installing and using the CPAN module YAPE::Regex::Explain (Tip #9 from Basic debugging checklist) 

    The regular expression:

(?-imsx:/(.*?\.gz)$)

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 (0 or more times
                             (matching the least amount possible))
----------------------------------------------------------------------
    \.                       '.'
----------------------------------------------------------------------
    gz                       'gz'
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

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Re: Why is this greedy matching?
by BrowserUk (Patriarch) on Mar 23, 2012 at 15:10 UTC

    If you don't want to capture any slashes, say that!:

    print 'http://txs.corp.com:8080/area/es/2215.csv.gz' =~ m[ ( [^/]+ $ )
+ ]x;;
2215.csv.gz

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    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.

    The start of some sanity?
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Re: Why is this greedy matching? (leftmost)
by tye (Sage) on Mar 23, 2012 at 14:48 UTC

    "First match" (leftmost) trumps "shortest match" (anti-greedy). You can use a greedy .* to replace "leftmost (sub)match" with "rightmost (sub)match" to end up with "shortest match" in cases like this: 

    m{.*/(.*\.gz)$}

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    Note that it doesn't matter whether you make the part inside the parens greedy or not here.

    - tye        

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Re: Why is this greedy matching?
by ww (Archbishop) on Mar 23, 2012 at 14:35 UTC
    ...perhaps because the deathstar in your capture matches everything after the second "/" in "http://"
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Re: Why is this greedy matching?
by JavaFan (Canon) on Mar 23, 2012 at 20:29 UTC
    Left most trumps non-greedy.
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