Ruby version Bash function

ruby-version.bash

# First parameter is a bash printf formatting string
# From second till fifth parameter, rvm-prompt format parameters
__ruby_ps1 () {
   if [ ! -f ./Rakefile ] &&
      [ "$(find -maxdepth 1 -name '*.rb' | head -n1)" == "" ]; then
      exit 1
   fi
   if [ -f ~/.rvm/bin/rvm-prompt ]; then 
      rst=$(~/.rvm/bin/rvm-prompt $2 $3 $4 $5)
   fi
   if [ -z "$rst" ]; then
      rst=$(ruby -v | cut -f2 -d' ')
   fi
   fmt="%s"
   if [ -n "$1" ]; then
      fmt="$1"
   fi
   if [ -n "$rst" ]; then
      printf "$fmt" "${rst}"
   fi
}