RosettaCodeData/Task/Find-common-directory-path/Perl/find-common-directory-path-1.pl

sub common_prefix {
    my $sep = shift;
    my $paths = join "\0", map { $_.$sep } @_;
    $paths =~ /^ ( [^\0]* ) $sep [^\0]* (?: \0 \1 $sep [^\0]* )* $/x;
    return $1;
}