#!/usr/bin/env perl

use strict;
use warnings;

use Path::Tiny;

my $filespec = "/usr/share/directory/piano_book.mp4";

my $path = path($filespec);
my $rel = $path->relative("/usr/share");
print $rel, "\n";
exit;
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How it can be done using regular expression?

If you really want to use regex, you could do this:

my $filespec = "/usr/share/directory/piano_book.mp4";
my $relative = "." . $1 if $filespec =~ m{/usr/share(.*)};
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Or you could use split and then paste together the pieces you need.

But you'd most probably be better off with a specialized module such as Path::Tiny mentioned above or some other.

How it can be done using regular expression?

You let Path::Tiny use File::Spec which uses regular expressions for you.

I would also advise using established modules for this, but here's another regex-only way to remove the first n directories from an absolute path. It looks like you're using a *nix path, and I haven't made the effort to define a proper directory pattern in  $dir (I don't think that any character other than a  / is allowed), so you will have to fix up the  [^/] character class accordingly.

c:\@Work\Perl\monks>perl -wMstrict -le
"my $filespec = '/usr/share/directory/piano_book.mp4';
 print qq{absolute: '$filespec'};
 ;;
 my $dir = qr{ / [^/]+ }xms;  # fix [^/]
 ;;
 my $n = 2;
 die qq{'$filespec' could not be made relative}
   unless $filespec =~ s{ \A (?: $dir){$n} }{.}xms;
 print qq{relative: '$filespec'};
"
absolute: '/usr/share/directory/piano_book.mp4'
relative: './directory/piano_book.mp4'
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Please see perlre, perlretut, and perlrequick.

Update: Added error check to substitution in example code.

---

Give a man a fish:  <%-{-{-{-<

use strict;
use warnings;
use File::Spec;

my(undef,$dir,$file)=File::Spec->splitpath( 'c:\Perl\bin\perl.exe' );

my @dirs = File::Spec->splitdir($dir);

# splitdir returns some '' empty dirs
# docs tell:
# Unlike just splitting the directories on the separator, empty direct
+ory names ('' ) can be returned,
# because these are significant on some OSes.
#
# infact adding
# use Data::Dump; dd @dirs;
# returns
# ("", "Perl", "bin", "")
# because of this i use the last one among those who contain something
# or (grep {/./} @dirs)[-1]

print File::Spec->catfile('',(grep {/./} @dirs)[-1],$file);

# the first empty '' passed to catfile is needed if you want the leadi
+ng separator
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L*

If what is wanted is really the lowest level directory plus file name, try this:

my $filespec = '/usr/share/directory/piano_book.mp4';
my @parts = split /\//, $filespec;
my $relative = './' . join '/', splice @parts,-2,2;
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