Shell Snippets

After finishing the Effective Shell Book I still find myself regularly discovering techniques that are huge time-savers. I've called these Effective Shell Snippets and will update this page with them from time to time, so check back regularly!

Git + AI: Interactively Staging Changes, Summarising with AI

A fun snippet I built is the function aigac - this is short for "AI Git Add & Commit". It performs an interactive patch add of changes to the working tree, commits the changes, then uses the Terminal AI tool to create a commit message with a title and description that follows conventional commit syntax:

The function looks like this:

https://github.com/dwmkerr/dotfiles/blob/main/shell.functions.d/aigac.sh

aigac() {
  # Add untracked files but none of their content - so that 'git add --patch'
  # lets us interactively stage new files as well as existing file changes.
  git add -N .
  git add --patch

  # If there's no changes, bail.
  if git diff --cached --quiet; then
    echo "No changes staged for commit."
    return 1
  fi

  # Generate the commit message using terminal-ai. Pipe it into 'git commit'
  # by using the '-F -' (i.e. read from the stdin file). Make sure we edit it
  # in the editor first with '-e'.
  git diff --cached |\
    ai -- 'summarise this git diff into a conventional commit, e.g. feat(feature): short description\n\nlong description' |\
    git commit -e -F - 
}

This snippet may change over time - you should be able to find the latest version in my dotfiles.

Open GitHub for Current Directory

When I'm working on some code I often want to open its GitHub home page, to check for issues, see the status of pipelines and so on. You can use the gh CLI for many of these operations, but if I just want to open the webpage, I like use the ghopen function:

This command will open the URL shown in your browser.

Here's the code:

https://github.com/dwmkerr/dotfiles/blob/main/shell.functions.d/ghopen.sh

ghopen() {
    # Get the origin for the current repo.
    local origin=$(git remote get-url origin 2> /dev/null)

    # Bail if we're not in a github repo.
    if [[ ($? -ne 0) || ("${origin}" != *github*) ]]; then
        echo "current dir '$(basename "${PWD}")' is not in a github repo..."
        return
    fi

    # The origin probably looks like this:
    # git@github.com:dwmkerr/effective-shell.git
    # The org/repo is everything after the colon and before '.git'.
    local org_repo=$(echo "${origin%.git}" | cut -f2 -d:)
    local url="http://github.com/${org_repo}"

    # Let the user know what we're opening, formatting org/repo in green, open.
    echo -e "opening github.com/\e[32m${org_repo}\e[0m"
    python3 -c "import webbrowser; webbrowser.open_new_tab('${url}')"
}

Some useful techniques - all of which are covered in various chapters across the book!

• Stream Redirection: We pipe errors from git to /dev/null so that we don't spam the user's screen, and check the result of the command with $?
• Conditionals: The Bash 'if statement' lets us check whether the origin contains the text 'github'
• Manipulating Text: The cut command can quickly cut out everything after the : in the origin
• Shell Expansion: We can use the ${origin%.git} brace expansion to remove .git from the end of a variable
• Opening a browser with python3 is more portable than using open or similar

tip

A super useful comment on Reddit on an alternative way to do this!

Makefile Help

This is a snippet I include in every Makefile that I use. It simply adds a default recipe called help that shows each recipe in the Makefile along with a description:

All you need to add to your Makefile is the recipe help shown below. To add a description to any other recipe just add a comment that follows its name!

default: help

.PHONY: help
help: # Show help for each of the Makefile recipes.
    @grep -E '^[a-zA-Z0-9 -]+:.*#'  Makefile | sort | while read -r l; do printf "\033[1;32m$$(echo $$l | cut -f 1 -d':')\033[00m:$$(echo $$l | cut -f 2- -d'#')\n"; done

.PHONY: example
example: # Here's an example of how to add a description!
    @echo "Hello!"

This is also documented in a little repo at github.com/dwmkerr/makefile-help.