The response FAILED open or read happens when the file specified in the md5 checksum file (md5sum.tmp in your case) does not exist.
For example.
[user@localhost tmp]$ cd /tmp/testfolder [user@localhost testfolder]$ touch dog [user@localhost testfolder]$ md5sum dog > /tmp/md5sum.tmp [user@localhost testfolder]$ md5sum -c /tmp/md5sum.tmp dog: OK [user@localhost testfolder]$ cd .. [user@localhost tmp]$ md5sum -c /tmp/md5sum.tmp md5sum: dog: No such file or directory dog: FAILED open or read md5sum: WARNING: 1 listed file could not be read Note that I believe the md5sum program does not look at the standard input when passed the -c option. It simply looks at the checksums in the file specified by the -c option. If they exist and the filename matches, than it compares it and all is happy.
While there is probably a better way, storing the result of two separate md5sums in a variable and then comparing them with an if statement is probably the approach I would take.
Kind of like this.
#!/bin/bash firstfile=`cat dog | md5sum ` secondfile=`cat mouse | md5sum ` if [ "$firstfile" == "$secondfile" ]; then echo "They Match!" else echo "They Don't Match!" fi