#!/usr/bin/perl

use strict;
use warnings;

use File::Spec;	# Note that test data is Unix-format!

warn "Test data is in Unix format; may not work on $^O"
  unless File::Spec->isa('File::Spec::Unix');

my @Files = map {chomp; $_} (<DATA>);

# find common prefix directories for a list of files; assuming that all
# files are on the same volume, if the system has volumes
sub common_prefix (@) {
  my @dirs = map {[File::Spec->splitdir((File::Spec->splitpath($_))[1])]} @_;

  my @prefix = @{shift @dirs};
  foreach my $dir (@dirs) {
    for (my $i = 0; $i < @$dir && $i < @prefix; $i++)
      { splice @prefix, $i unless $dir->[$i] eq $prefix[$i] }
  }

  return @prefix
}

print "Sample files:\n";
print '  ',$_,"\n" for @Files;

print "Common prefix:\n";
print '  ',File::Spec->catdir(common_prefix @Files),"\n";

__DATA__
/foo/bar/bax
/foo/bar/baz
/foo/baz/quux

##</code><code>##

Sample files:
  /foo/bar/bax
  /foo/bar/baz
  /foo/baz/quux
Common prefix:
  /foo