bash code to open a PR

pr.sh

# NOTE: Apologies to anyone who actually speaks bash, because I'm sure all the comments
# here feel annoyingly obvious. As someone who writes bash once in a blue moon, I find it
# helpful to leave myself extensive hints so future-me has any clue what current-me 
# has written.

# This code lives in my `.zshrc` and makes it so that I can run `git push && pr` and a new
# PR will open in my browser. Notably, it uses `origin` as a base, which solves the problem
# discussed in https://github.com/orgs/community/discussions/11729.

# get origin's default branch and then strip off the "origin/" prefix 
alias get_main_branch='git rev-parse --abbrev-ref origin/HEAD | sed s/"origin\/"//'


# NOTE: This accounts for detached heads because I also use it to set my prompt.
# If you're just using it for `get_compare_url`, you can just use 
# `git rev-parse --abbrev-ref HEAD` instead of this function.
function get_current_branch() {
  # If we're in a git repo, HEAD will resolve to something and the exit
  # status of git rev-parse will be 0 (good); otherwise, it will be 128
  # (bad). Negate that so that if we're not good (not in a git repo), we
  # can bail. (The parens run the command in a sub-shell, and the &> sends
  # both stdout and stderr to /dev/null.)
  if ! (git rev-parse HEAD &>/dev/null); then
    return
  fi

  # so now we know were in a repo, so get the branch name (the $() captures
  # the stdout of the command inside the parens)
  local git_branch=$(git rev-parse --abbrev-ref HEAD)

  # If we've checked out a particular commit, the HEAD has no other --abrev-ref
  # besides "HEAD." In that case, change the "branch name" to say so. (The [[ ]]
  # are for capturing the boolean value of a statement.)
  if [[ $git_branch == "HEAD" ]]; then
    # in a `git log` command, -n <num> shows you only the most recent <num>
    # commits, and in the format string, "%h" is the short form of the
    # commit sha
    git_branch="Detached HEAD at $(git log -n 1 --format="%h")"
  fi

  # since you can't return anything from a bash/zsh function, echo the result
  # and then capture it on the other end with $()
  echo $git_branch
}

function get_repo_url() {
  #get names of remotes - should be "origin" - and take the first one in case there's more than one
  #(head -n <x> gives you the first <x> lines of output)
  local remote_name=$(git remote | head -n 1)

  #url should be of the form https://github.com/<gh-org-name>/<gh-repo-name>.git
  #use sed to remove the .git (-E makes sed use "extended" regexes)
  #(because git prints to stdout, we don't need to echo here)
  git remote get-url ${remote_name} | sed -E s/\\.git//

}

function get_compare_url() {
  # this assumes the branch is of the form `xyz` or `abc/xyz`, and returns `xyz` in either case
  local branch_basename=$(basename $(get_current_branch))

  local repo_url_base=$(get_repo_url)

  echo "${repo_url_base}/compare/$(get_main_branch)...${branch_basename}"
}

function pr() {
  local branch_name=$(git rev-parse --abbrev-ref HEAD)

  # see if a PR already exists. If it does, it should be listed in `.git/config` under `branch.<branch-name>.github-pr-owner-number`, 
  # in the form `<gh-org>#<gh-repo>#<PR-number>`. Pipe that to sed (using `-E` to be able to use regular regexes) to pull off the first 
  # two `<...>#` segments, leaving just the number.
  local PR_num=$(git config branch.${branch_name}.github-pr-owner-number | sed -E 's/([^#]+#){2}//')

  if [[ -n "$PR_num" ]]; then
    local pr_url=$(get_repo_url)/pull/$PR_num
    echo "\nOpening existing PR: $pr_url."
    open $pr_url
    return
  fi

  # using the "${repo_url_base}/pull/new/${branch_name}" url recommended in the
  # git output after running `git push`` just gets you redirected to
  # "${repo_url_base}/compare/${branch_name}?expand=1", so we can reuse the
  # url we computed for the `compare` function above
  echo "\nNo existing PR found. Opening a new one."
  open "$(get_compare_url)?expand=1"
}