prezto_config/plugins/git/functions/git-hub

# Open the GitHub repository in the browser.
local remote branches branch current_branch url

remote="${1:-origin}"
url=$(
  git config -l \
    | grep "remote.${remote}.url" \
    | sed -En "s/remote.${remote}.url=(git|https?)(@|:\/\/)github.com(:|\/)(.+)\/(.+).git/https:\/\/github.com\/\4\/\5/p"
)
branches=($(
  git branch -r | sed -e "/${remote}\/HEAD -> ${remote}/d" -e "s/^[[:space:]]*${remote}\///g"
))
current_branch="$(git-branch)"
branch="${2:-master}"

if [[ -z "$2" ]]; then
  if (( $branches[(I)$current_branch] != 0 )); then
    branch="$current_branch"
  else
    branch='master'
  fi
fi

if [[ -n "$url" ]]; then
  url="${url}/tree/${branch}"

  if (( $+commands[$BROWSER] )); then
    "$BROWSER" "$url"
    return 0
  else
    print "$0: browser not set or set to a non-existent browser" >&2
    return 1
  fi
else
  print "$0: not a Git repository or remote origin not set" >&2
  return 1
fi