#!/usr/bin/perl -w
use strict;

my @teststr = (
"32977186    4 -rw-r--r--   1 owner   mygrp   65 Aug  4 13:16 /long/path/to/my/file/file1.txt",
"32977186    4 -rw-r--r--   1 owner   mygrp   65 Aug  4 13:16 /long/path/to/my/file/file2.txt",
"32977186    4 -rw-r--r--   1 owner   mygrp   65 Aug  4 13:16 /long/path/to/my/file/file3.txt",
"32977186    4 -rw-r--r--   1 owner   mygrp   65 Aug  4 13:16 /long/path/to/my/file/file4.txt",
);

my %testhash = map { m{(([^/]+)\.[^/]+)$}; $2, $1 } @teststr;

print "$_ => $testhash{$_}\n" for sort keys %testhash;