You can configure your IRB sessions to provide tab completion, and
other neat things. A page here: http://tinyurl.com/fkuj2 gives
details, but the code there can be improved with a few Ruby idioms.
Here’s what’s in mine:
IRB.conf[:AUTO_INDENT] = true
IRB.conf[:USE_READLINE] = true
IRB.conf[:LOAD_MODULES] ||= 
IRB.conf[:LOAD_MODULES] |= [‘irb/completion’]