#!/usr/local/bin/perl

use strict;
use warnings;

my @lines_ok = ();

while (<DATA>) {
    chomp;
    pop @lines_ok, next if /fail/;
    push @lines_ok, $_;
}
print join(", ", @lines_ok);

__DATA__
line 1
line 2
line 3
fail
line 4
line 5