You know, you could simply do:

while (<>) {
    next if !/p/;
    next if !/e/;
    next if !/r/;
    next if !/l/;
    print;
}
[download]

or (if you don't mind using unless)...

while (<>) {
    next unless /p/;
    next unless /e/;
    next unless /r/;
    next unless /l/;
    print;
}
[download]