Basic Oh My Zsh plugin to switch between PHP versions on Debian-based systems.

php-switcher.plugin.zsh

function switch_php_to() {
  if [ -z "$1" ]; then
    echo "Please specify PHP version first!"
    return 1
  else
    command -v php || return 1

    local CURRENT_PHP_VERSION=$(get_current_php_version)
    
    if [ $1 == $CURRENT_PHP_VERSION ]; then
      echo "PHP $1 is already loaded."
      return 0
    elif [ $(command -v php$1) ]; then
      setup_php_version $1
    else
      install_php $1 && setup_php_version $1
    fi

    echo "All done!"
  fi
}

function get_current_php_version() {
  php -r "echo substr(PHP_VERSION, 0, 3);"
}

function install_php() {
  if [ -z "$1" ]; then
    echo "Please specify PHP version first!"
    return 1
  else
    echo "Installing php$1"
    local PACKAGE_MANAGER_INTERFACE="apt-get"

    if [ $(command -v aptitude) ]; then
      echo -n "You have aptitude installed locally on your machine, use it instead of the apt-get? (y/n)? "
      read answer
      if [ "$answer" != "${answer#[Yy]}" ]; then
        PACKAGE_MANAGER_INTERFACE="aptitude"
      fi
    fi

    sudo $PACKAGE_MANAGER_INTERFACE update
    sudo $PACKAGE_MANAGER_INTERFACE install php$1 || return 1
  fi
}

function setup_php_version() {
  if [ -z "$1" ]; then
    echo "Please specify PHP version first!"
    return 1
  else
    echo "Setup php to version $1."
    sudo update-alternatives --set php /usr/bin/php$1
    sudo update-alternatives --set phar /usr/bin/phar$1
    sudo update-alternatives --set phar.phar /usr/bin/phar.phar$1 
    sudo update-alternatives --set phpize /usr/bin/phpize$1
    sudo update-alternatives --set php-config /usr/bin/php-config$1
  fi
}

is not ready to use, right?

Hi 👋 Ready as far as you have updated repository with access to older php versions. You can rely (sudo add-apt-repository ppa:ondrej/php) on ppa:ondrej/php repository for instance. Now I am working on Ubuntu 20 and to solve issues with different php version I just use docker for it 😉 but on my latest 18.04 ubuntu version everything was ok with this plugin.