Based on the correction you've described above, what you're really looking for is way to say "match the whole word". You can do that by specifying boundaries (note, this is untested):

$words = "\b(directory|file|age|action)\b";
# A little more Perl-ish:
while (<>)
{
    print "Couldn't find $_\n" unless /$words/;
}
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You can read more about \b in perlre.