#!/usr/bin/env perl

use strict;
use warnings;

while (my $init_line = <DATA>) {
    my $neg_class_line = $init_line;
    my $neg_assert_line = $init_line;

    $neg_class_line  =~ s/,([^,]*)$/$1/;
    $neg_assert_line =~ s/,(?!.*,)//;

    print 'Initial line:       ', $init_line;
    print 'Negated class:      ', $neg_class_line;
    print 'Negative assertion: ', $neg_assert_line;
    print '-' x 40, "\n";
}

__DATA__
21112,/vol/voly,blx
21113,/vol/eng,blz
21114,/vol/eng,file