After reading codes and searching on google, I have developed my own
little script to add auto complete for rake/cap to display available
tasks.It’s only for bash shell.
I will add capistrano-ext for cap completion to get stages completion
if it’s possible.
Source code is on github:http://github.com/sgruhier/
rake_cap_bash_autocomplete/tree/master but you do not need to clone
the repository, just copy/paste the shell script.