#!/usr/bin/perl
use warnings;
use strict;
use feature qw(say);

my $filename            = 'p_abc_xyz_123.txt';
my ($basename, $suffix) = split /\./, $filename;
my @parts               = split /_/,  $basename;

for my $i (1 .. $#parts) {
    say join('_', @parts[0 .. $i]), ".$suffix";
}