## Ranges of characters are used; [a-m] expands to abcdefghijklm
## and will be replaced by the corresponding character in the range [n-z]
## Each letter in the first half of the alphabet is replaced by
## a letter from the second half, and vice versa.
cat "$@" | tr '[a-m][A-M][n-z][N-Z]' '[n-z][N-Z][a-m][A-M]'
