#!/bin/sh

# Accepts filenames either on the command line, or if the command line
# is empty, as a null-separated list of filenames on stdin.

MD5S="`mktemp`"

if (( $# > 0 ));then 
  md5sum "$@" 
else
  xargs -0 md5sum
fi > "$MD5S"

< "$MD5S" awk '{ print $1 }'	|
sort				|
uniq -d				|
fgrep -f - "$MD5S"		|
sort

rm "$MD5S"