gistfile1.rb

#!/usr/bin/env ruby

# To use, put this in your bashrc:
# complete -C path/to/script -o default your_command_or_commands_here
#   example, to complete the foo and bar commands with the foo.rb script: complete -C ~/bin/foo.rb -o default foo bar

prefix = ARGV[1] 

words = `some command here, or just any array`.split.uniq
words = words.select {|w| /^#{Regexp.escape prefix}/ =~ w} if prefix

puts words