Many UNIX utilities allow you to give an input filename on the command line or just pipe to STDIN. For example, these are equivalent:

less foo.txt
cat foo.txt | less

I would like coderay to take the input from STDIN if one is not given on the command-line. This would be particularly helpful with diff output:

diff -U1 foo.txt bar.txt | coderay -diff

This would be useful in conjunction with #111: Add smart detection of input language