#!/usr/bin/env perl -l

use strict;
use warnings;

use File::Basename;

my @paths = qw{hhk_1sss-(hello).txt hhk_2abc-(hello).txt hhk_3xyz-(hello).txt};
my @split_paths = map { [ fileparse($_ => qr{[.]?[^.]*}) ] } @paths;
my @names = map { $split_paths[$_][0] } 0 .. $#split_paths;
my $common_start = get_common(@names);
my $common_end = reverse get_common(map { scalar reverse } @names);

for (@split_paths) {
    print +($_->[0] =~ /^\Q$common_start\E(.*)\Q$common_end\E$/)[0], $_->[2];
}

sub get_common {
    my ($control, $compare, @rest) = @_;
    my $common = '';
    my ($control_len, $compare_len) = map { length } $control, $compare;

    for (0 .. ($control_len < $compare_len ? $control_len : $compare_len) - 1) {
        my $control_char = substr $control, $_, 1;
        last if $control_char ne substr $compare, $_, 1;
        $common .= $control_char;
    }

    return @rest ? get_common($common, @rest) : $common;
}

##</code><code>##

$ pm_ex_same_strings.pl
1sss.txt
2abc.txt
3xyz.txt