First off, this is licensed under the GPLv2, you can find a copy of it in the file called LICENSE.
Second off, you could easily change this to take an argument of the offset to make it a proper Caesar Cypher.
echo WOOP | ./vogon_translator
are the same.
Piping the input in is preferred, however, as you can then do:
cat Jabberwocky | ./vogon_translator
the rest is self explanatory :)
I've included Jabberwocky so that you can try this for yourself :)
This requires unistd.h to run, although the compiled version should work on any Linux box just fine.
NB: Sorry for the horrible coding, I made this at about 2:00 -> 3:00 with no caffeine.