prezto_config/modules/git/functions/git-hub-browse

#
# Opens a GitHub repository in the default browser.
#
# Authors:
#   Sorin Ionescu <sorin.ionescu@gmail.com>
#

local remotes remote references reference file url

remote="${1:-origin}"
remotes=($(git config --get-regexp 'remote.*.url' | cut -d. -f2))

if (( $remotes[(i)$remote] == $#remotes + 1 )); then
  print "$0: remote not found: $remote" >&2
  return 1
fi

url=$(
  git config --get "remote.${remote}.url" \
    | sed -En "s/(git|https?)(@|:\/\/)github.com(:|\/)(.+)\/(.+).git/https:\/\/github.com\/\4\/\5/p"
)

reference="${${2:-$(git-branch-current)}:-HEAD}"
references=(
  HEAD
  ${$(git ls-remote --heads --tags "$remote" | awk '{print $2}')##refs/(heads|tags)/}
)

if (( $references[(i)$reference] == $#references + 1 )); then
  print "$0: branch or tag not found: $reference" >&2
  return 1
fi

if [[ "$reference" == 'HEAD' ]]; then
  reference="$(git rev-parse HEAD 2>/dev/null)"
fi

file="$3"

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

  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 not set" >&2
  return 1
fi