Re: [Trisquel-users] sudo: add-apt-repository: command not found

[legimet . calc]

That command is in the package "python-software-properties". You should  
already have it, but if you don't, then install (if you don't have it) or  
reinstall that package.

If you don't have it:
 $ sudo apt-get install python-software-properties
If you do have it reinstall with:
 $ sudo apt-get install --reinstall python-software-properties