rot13 on all names of files in a directory!
Not really an Android question (rather Linux/Shell/Bash), but I give the credit of the missing executable. So:

for i in * ; do j=`echo $i | tr '[a-m][n-z][A-M][N-Z]' '[n-z][a-m][N-Z][A-M]'`; mv "$i" "$j"; done