Shell function that's a shortcut interface to rbenv to quickly pick & switch between Ruby versions

readme.md

rbenv is great, but switching between Ruby versions with it is kind of a pain since you have to specify full version names all the time. Example:

# change version in shell:
$ rbenv shell ree-1.8.7-2012.02
# run command:
$ RBENV_VERSION=jruby-1.6.7.2 rake something
# enable 1.9 mode:
$ RBENV_VERSION=rbx-2.0.0-dev RBXOPT=-X19 ruby -v

rb() is a shell function that fixes this.

$ rb ree
$ rb jr rake something
$ rb rbx 19 ruby -v

The short version specifier you give is matched against all available versions with grep, and the last match is picked. This means if you say "1.8", it will pick a 1.8.7 version over 1.8.6 if you have both installed. To make it explicit you want 1.8.6, simply say "1.8.6" or just "8.6".

rb.sh

# Shortcut interface to rbenv to quickly pick & switch between Ruby versions.
# Usage:
#   rb <version> [19]
#   rb <version> [19] <command>...
#   rb
#
# A version specifier can be a partial string which will be matched against
# available versions and the last match will be picked. The optional "19"
# argument switches JRuby or Rubinius to 1.9 mode.
#
# When no arguments are given, the current ruby version in the shell is reset
# to default.
#
# Examples:
#   rb 1.8
#   rb ree
#   rb rbx irb
#   rb rbx 19 ruby -v
#   rb jr 19 rake something
#
rb() {
  if [[ $# -lt 1 ]]; then
    rbenv shell --unset
    # warning: potentially destructive to user's environment
    unset RBXOPT
    unset JRUBY_OPTS
  else
    local ver="$(rbenv versions --bare | grep "$1" | tail -1)"
    if [[ -z $ver ]]; then
      echo "no ruby version match found" >&2
      return 1
    else
      shift
      if [[ $1 == 19 ]]; then
        local rbx_opt="RBXOPT=-X19"
        local jrb_opt="JRUBY_OPTS=--1.9"
        shift
      fi

      if [[ $# -gt 0 ]]; then
        env RBENV_VERSION="$ver" $rbx_opt $jrb_opt "$@"
      else
        [[ -n $rbx_opt || -n $jrb_opt ]] && export $rbx_opt $jrb_opt
        rbenv shell "$ver"
      fi
    fi
  fi
}

usage.sh

$ ruby -v 
ruby 1.9.3p194

$ rbenv versions
  1.9.2-p320
  1.9.3-p0
* 1.9.3-p194 (set by /Users/mislav/.rbenv/version)
  jruby-1.6.7.2
  rbx-1.2.4
  rbx-2.0.0-dev
  ree-1.8.7-2012.02

$ rb 1.8 ruby -v
ruby 1.8.7, Ruby Enterprise Edition 2012.02

$ rb rbx ruby -v
rubinius 2.0.0dev (1.8.7)

$ rb rbx 19 ruby -v
rubinius 2.0.0dev (1.9.3)

$ rb jr ruby -v
jruby 1.6.7.2 (ruby-1.8.7-p357)

$ rb jr 19 ruby -v
jruby 1.6.7.2 (ruby-1.9.2-p312)

# change rbenv version for current shell
$ rb rbx
$ ruby -v
rubinius 2.0.0dev (1.8.7)
# reset it to default version
$ rb
$ ruby -v
ruby 1.9.3p194

cd ~/.rbenv/versions
ln -s rbx-1.2.4 rbx
rbenv shell rbx

@MBO: nice. However, won't now rbenv version list more versions than you have?

@mislav You're right, that's problem with how rbenv lists installed versions by just listing content of versions directory. Worth to mention. I haven't thought about it because I rarely list versions.