Ubuntu – shell script to conditionally add apt repository

Use output redirection to /dev/null and include stderr output.

add-apt-repository -y ppa:ondrej/php5-oldstable > /dev/null 2>&1

• The 2>&1 will tell Bash to redirect stderr to stdout.
• The command > file stanza will redirect stdout to a file, in this case /dev/null.
• /dev/null is the black hole of Linux - you won't be able to recovery anything from there.

Result: full silent execution of your command.

In your updated question you seem to log all output to a file. In that case you can just append the 2>&1 to your current line:

add-apt-repository -y ppa:ondrej/php5-oldstable >> /tmp/output.txt 2>&1

This is because you were looking at the stderr output being printed on the terminal, which you need to redirect to the log as well (otherwise you will miss out on all errors!).

That is a bash function, and to pass arguments to bash functions, you don't need (). Also, the function adds the ppa: prefix to its arguments, so just this would do:

add_ppa otto-kesselgulasch/gimp-edge

Additionally, the function supports multiple arguments, so you can run it for multiple PPAs:

add_ppa otto-kesselgulasch/gimp-edge foo/bar a/b

Given that you have put the function in a script, you should either:

• source it as Zanna suggests to get the function in your shell and call the function, or

• just use the contents of the function as the script:

  #! /bin/bash
  for i in "$@"; do
    if grep -Rq "^deb.*$i" /etc/apt/sources.list.d/*.list
    then
      echo "Adding ppa:$i"
      sudo add-apt-repository -y ppa:$i
    else
      echo "ppa:$i already exists"
    fi
  done
  

  And the call the script with the ppa name:

  ppa otto-kesselgulasch/gimp-edge