Custom Preexec Function in zsh

In zsh, there exists Hook Functions, and one of these Hook Functions is the preexec function. The preexec function is executed just after a command has been read and before it has been executed. In zsh, we can define a custom prexec function in the .zshrc configuration.

I will show how I utilized the prexec function to prompt for extra confirmation before running certain commands. This custom function will help me to think twice before running critical commands, for instance, commands targeting a production Kubernetes cluster.

In .zshrc,

# Hooks

pre_validation() {
  # Get the current command
  local current_cmd=$(echo $1 | xargs)

  # Match the command against regexes
  if [[ "$current_cmd" =~ ^"rm -rf" ]] || \
     [[ "$current_cmd" =~ ^"git reset --hard HEAD" ]] || \
     [[ "$current_cmd" =~ ^"git add ." ]] || \
     [[ "$current_cmd" =~ .*"prod".* ]]; then
	echo "THIS COMMAND MATCHED THE DANGER FILTER! PLEASE CONFIRM THAT THE COMMAND SHOULD RUN."
	echo "[ANY] = confirm [Ctrl+c] = decline"
	read -sk key
  fi
}

The function is simple,

1. Read the input command
2. Match the command against regexes
3. If the command matches any of the regexes
   1. Show a warning text
   2. Wait for user input by read -sk key which gives the user the possibility to send the SIGINT signal by Ctrl + c, hence terminating the process

To activate the custom preexec function, add these two lines the .zshrc and then run source ~/.zshrc

autoload -U add-zsh-hook                  # Load the zsh hook module
add-zsh-hook preexec pre_validation       # Adds the pre-hook

To deactivate the custom preexec function we need to add the following line

add-zsh-hook -d preexec pre_validation

Examples

Hopefully, this will help me to overcome the bad habit of running git add .