Gfilui

I'm creating a bash script to install automatically the last stable version of ruby without root privileges. This is what I have so far:

#Install GPG Keys
curl -sSL https://rvm.io/mpapis.asc | gpg2 --import

#Install RVM
curl -sSL https://get.rvm.io | bash -s -- --ignore-dotfiles
echo "source $HOME/.rvm/scripts/rvm" >> ~/.bash_profile

#Set environment
source $HOME/.rvm/scripts/rvm

#Install Ruby
rvm install $RUBY_VERSION

I need to find the last stable Ruby version to set RUBY_VERSION variable.

Assuming the last stable version is always the last file with a filename like ruby-2.5.1.tar.gz on https://cache.ruby-lang.org/pub/ruby/, you can extract the version number with:

curl -s https://cache.ruby-lang.org/pub/ruby/ | sed -nr '1h;1!H;$!d;x;s/.*ruby-([0-9.]+).tar.gz.*/1/p'

This approach uses curl to retrieve the file list and GNU sed to cut out the version number as explained in this SO answer. You could also use grep with lookarounds instead, it even may be slightly faster:

curl -s https://cache.ruby-lang.org/pub/ruby/ | grep -oP '(?<=ruby-)d.d.d(?=.tar.gz)' | tail -1

Just add a line setting the RUBY_VERSION variable to your script:

#Get version number of latest stable Ruby version
RUBY_VERSION=$(curl -s https://cache.ruby-lang.org/pub/ruby/ | sed -nr '1h;1!H;$!d;x;s/.*ruby-([0-9.]+).tar.gz.*/1/p')

#Install Ruby
rvm install $RUBY_VERSION

Example run

$ curl -s https://cache.ruby-lang.org/pub/ruby/ | sed -nr '1h;1!H;$!d;x;s/.*ruby-([0-9.]+).tar.gz.*/1/p'
2.5.1
$ curl -s https://cache.ruby-lang.org/pub/ruby/ | grep -oP '(?<=ruby-)d.d.d(?=.tar.gz)' | tail -1
2.5.1