Defining Ruby's path version by update-alternatives tool

ruby_update-alternatives.sh

#!/bin/bash
#
# By: Samuel Maciel Sampaio <samukasmk@gmail.com> [20140328]
# Defining Ruby's version by alternatives tool

# Set the ruby version you want to configure
RUBY_VERSION="1.8"


ALTERNATIVES_TOOL=$(which update-alternatives 2>/dev/null)
if [ -z "$ALTERNATIVES_TOOL" ];
then
    ALTERNATIVES_TOOL=$(which alternatives 2>/dev/null)
    if [ -z "$ALTERNATIVES_TOOL" ];
    then
        echo "Error: Unable to find 'alternatives' program... please install them or put in your \$PATH"
    fi
fi

ALTERNATIVES_PRIORITY="99999999"

${ALTERNATIVES_TOOL} --install /usr/bin/ruby ruby /usr/bin/ruby${RUBY_VERSION} ${ALTERNATIVES_PRIORITY} \
  --slave /usr/bin/rdoc rdoc /usr/bin/rdoc${RUBY_VERSION} \
  --slave /usr/bin/ri ri /usr/bin/ri${RUBY_VERSION} \
  --slave /usr/bin/irb irb /usr/bin/irb${RUBY_VERSION} \
  --slave /usr/bin/erb erb /usr/bin/erb${RUBY_VERSION} \
  --slave /usr/bin/testrb testrb /usr/bin/testrb${RUBY_VERSION} \
  --slave /usr/bin/gem gem /usr/bin/gem${RUBY_VERSION} \
  --slave /usr/bin/rake rake /usr/bin/rake${RUBY_VERSION} \
  --slave /usr/share/man/man1/ruby.1.gz ruby.1 /usr/share/man/man1/ruby${RUBY_VERSION}.1.gz \
  --slave /usr/share/man/man1/rdoc.1.gz rdoc.1 /usr/share/man/man1/rdoc${RUBY_VERSION}.1.gz \
  --slave /usr/share/man/man1/ri.1.gz ri.1 /usr/share/man/man1/ri${RUBY_VERSION}.1.gz \
  --slave /usr/share/man/man1/testrb.1.gz testrb.1 /usr/share/man/man1/testrb${RUBY_VERSION}.1.gz \
  --slave /usr/share/man/man1/rake.1.gz rake.1 /usr/share/man/man1/rake${RUBY_VERSION}.1.gz \
  --slave /usr/share/man/man1/irb.1.gz irb.1 /usr/share/man/man1/irb${RUBY_VERSION}.1.gz \
  --slave /usr/share/man/man1/erb.1.gz erb.1 /usr/share/man/man1/erb${RUBY_VERSION}.1.gz \
  --slave /usr/share/man/man1/gem.1.gz gem.1 /usr/share/man/man1/gem${RUBY_VERSION}.1.gz 

${ALTERNATIVES_TOOL} --set ruby /usr/bin/ruby${RUBY_VERSION}

${ALTERNATIVES_TOOL} --display ruby

echo "Current ruby version: `ruby --version`"