snippet merlyn A challenge was made in <a href="news:comp.unix.shells">comp.unix.shells</a> for a short program to detect common lines in both <tt>fileA</tt> and <tt>fileB</tt>, printing one copy of each of common lines. Of course, this was a natural one-liner in Perl, but I stumbled across a bizarre way which I though you might appreciate. <CODE> perl -ne 'print if ($seen{$_} .= @ARGV) =~ /10$/' fileA fileB >output </CODE>