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perl -lne 'exists $h{$_} ? print "$_ in $h{$_} and $ARGV" : ($h{$_} = +$ARGV)' file1 file2
perl -F: -lane 'exists $h{$F[2]} ? print "$F[2] in $h{$F[2]} and $ARGV +" : ($h{$F[2]} = $ARGV)' passwd1 passwd2