grep using the recursive option

[worthspending]

The following work as expected.

# search everything in the current directory

grep index *

# search all files with an .rb extension

grep index *.rb

# search everything in the current directory and recursively through sub-directories

grep -r index *

# this one does not work

grep -r index *.rb

I can only seem to get the -r option to work if I use * for everything.

I don't understand.