G'day ovedpo15,

I think your biggest problem here is that you've immediately reached for a regex solution. When I first saw the question title, before even looking at the content, my first thought was rindex and substr.

Perl's string handling functions (and operators) are, in my experience, substantially faster than achieving the same functionality with regexes. There are times when a regex is appropriate; however, often it's not the best solution.

So, rather than making guesses and assumptions, let's Benchmark.

#!/usr/bin/env perl

use 5.010;
use strict;
use warnings;

use constant {
    PATH => 0,
    VERSION => 1,
    WANT => 2,
};

use Benchmark 'cmpthese';
use Test::More;

my @tests = (
    [qw{
        /a/b/version1/c/d
        version1
        /a/b/version1
    }],
    [qw{
        /some/path/3.5.2+tcl-tk-8.5.18+sqlite-3.10.0/a/b/c
        3.5.2+tcl-tk-8.5.18+sqlite-3.10.0
        /some/path/3.5.2+tcl-tk-8.5.18+sqlite-3.10.0
    }],
);

plan tests => 2*@tests;

for my $test (@tests) {
    is _regex(@$test[PATH, VERSION]), $test->[WANT];
    is _rindex(@$test[PATH, VERSION]), $test->[WANT];
}

cmpthese 0 => {
    regex0 => sub { _regex(@{$tests[0]}[PATH, VERSION]); },
    regex1 => sub { _regex(@{$tests[1]}[PATH, VERSION]); },
    rindex0 => sub { _rindex(@{$tests[0]}[PATH, VERSION]); },
    rindex1 => sub { _rindex(@{$tests[1]}[PATH, VERSION]); },
};

sub _regex {
    my ($path, $version) = @_;

    $path =~ s/.*\Q$version\E\K.*//s;

    return $path;
}

sub _rindex {
    my ($path, $version) = @_;

    $path = substr $path, 0, length($version) + rindex $path, $version
+;

    return $path;
}
[download]

The Test::More code is just to ensure the functions are producing correct results; which they are. The output from that is identical in all runs, so I'll just post it once:

1..4
ok 1
ok 2
ok 3
ok 4
[download]

I ran the benchmark five times. Here's the sections of output that relate to that:

             Rate  regex1  regex0 rindex0 rindex1
regex1   809214/s      --     -7%    -69%    -75%
regex0   866627/s      7%      --    -67%    -73%
rindex0 2632175/s    225%    204%      --    -19%
rindex1 3257343/s    303%    276%     24%      --

             Rate  regex1  regex0 rindex0 rindex1
regex1   825777/s      --     -5%    -68%    -75%
regex0   870952/s      5%      --    -66%    -73%
rindex0 2579956/s    212%    196%      --    -21%
rindex1 3261289/s    295%    274%     26%      --

             Rate  regex1  regex0 rindex0 rindex1
regex1   807841/s      --     -8%    -69%    -75%
regex0   880657/s      9%      --    -66%    -73%
rindex0 2625422/s    225%    198%      --    -20%
rindex1 3265104/s    304%    271%     24%      --

             Rate  regex1  regex0 rindex0 rindex1
regex1   807626/s      --     -7%    -69%    -75%
regex0   873101/s      8%      --    -66%    -73%
rindex0 2567429/s    218%    194%      --    -21%
rindex1 3255180/s    303%    273%     27%      --

             Rate  regex1  regex0 rindex0 rindex1
regex1   827447/s      --     -6%    -68%    -75%
regex0   877972/s      6%      --    -66%    -73%
rindex0 2579110/s    212%    194%      --    -21%
rindex1 3260240/s    294%    271%     26%      --
[download]

Do you still want to go with a regex solution? :-)

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