PS1 with low latency git branch detection

.jartps1.sh

#!/bin/bash
# jartps1.sh - Enhanced bash prompt
# Author: Justine Tunney <jart@google.com>
# Modified: 2023-11-28
#
# LIST OF BASH PROMPT ENHANCEMENTS
#
#   - No latency issues when holding down enter key
#   - Doesn't look unfamiliar compared to bash defaults
#   - Show current git branch
#   - Show background job count if \j > 0
#   - Show process exit code if $? != 0
#
# TRY IT OUT
#
#   JARTPS1_THEME=dark source .jartps1.sh
#
# CUSTOMIZING
#
#   Copy/paste the `PS1="..."` line from this file and add it to your bashrc
#   after the line where you source this file and refer to the `man bash`
#   section titled "PROMPTING".
#
#   If you're using a black background terminal then you might want to
#   customize the color and make things look more fabulous. You just have to
#   figure out the ANSI escape codes for the colors you want. Don't remove the
#   0's because they're used to reset the current formatting. Also don't remove
#   the \[...\] escapes or else bash will print artifacts when you do things
#   like reverse search. A library called Fabulous will help you generate the
#   escape codes:
#
#     $ sudo apt-get install python-pip
#     $ sudo pip install fabulous
#     $ python
#     >>> from fabulous import color
#     >>> color.red('hello')
#     u'\x1b[31mhello\x1b[39m'
#     >>> color.fg256('#ff6699', 'hello')
#     u'\x1b[38;5;204mhello\x1b[39m'
#     >>> color.bold(color.flip(color.fg256('indianred', 'hello')))
#     u'\x1b[1;7;38;5;167mhello\x1b[39;27;22m'
#
#   See also: https://github.com/jart/fabulous/blob/master/fabulous/color.py
#
# NOTES
#
#   This script will leave a tiny temp file behind for each terminal you
#   open. This isn't a problem because `/etc/cron.daily/tmpreaper` will delete
#   them after seven days or so.
#
# CHANGELOG
#
#   2023-11-28  Justine Tunney  <jart@google.com>
#
#     * Support shells other than bash
#     * Support /Users convention on MacOS
#
#   2014-06-20  Justine Tunney  <jart@google.com>
#
#     * Conform to go/bashstyle
#
#   2013-12-10  Justine Tunney  <jart@google.com>
#
#     * Fixed a bug which caused bash to display a warning each time the prompt
#       is displayed if a certain /tmp file got deleted by a weekly cleanup
#       cron job.
#
#     * Fixed ps1_error() and ps1_jobs() now that I understand bash arithmetic
#       expressions better.
#

ps1_error() {
  local e=$?
  if [ $e -ne 0 ]; then
    case $e in
      129) printf "\$?=SIGHUP "    ;;
      130) printf "\$?=SIGINT "    ;;
      131) printf "\$?=SIGQUIT "   ;;
      132) printf "\$?=SIGILL "    ;;
      133) printf "\$?=SIGTRAP "   ;;
      134) printf "\$?=SIGABRT "   ;;
      135) printf "\$?=SIGBUS "    ;;
      136) printf "\$?=SIGFPE "    ;;
      137) printf "\$?=SIGKILL "   ;;
      138) printf "\$?=SIGUSR1 "   ;;
      139) printf "\$?=SIGSEGV "   ;;
      140) printf "\$?=SIGUSR2 "   ;;
      141) printf "\$?=SIGPIPE "   ;;
      142) printf "\$?=SIGALRM "   ;;
      143) printf "\$?=SIGTERM "   ;;
      145) printf "\$?=SIGCHLD "   ;;
      146) printf "\$?=SIGCONT "   ;;
      147) printf "\$?=SIGSTOP "   ;;
      148) printf "\$?=SIGTSTP "   ;;
      149) printf "\$?=SIGTTIN "   ;;
      150) printf "\$?=SIGTTOU "   ;;
      151) printf "\$?=SIGURG "    ;;
      152) printf "\$?=SIGXCPU "   ;;
      153) printf "\$?=SIGXFSZ "   ;;
      154) printf "\$?=SIGVTALRM " ;;
      155) printf "\$?=SIGPROF "   ;;
      156) printf "\$?=SIGWINCH "  ;;
      157) printf "\$?=SIGIO "     ;;
      159) printf "\$?=SIGSYS "    ;;
      *)   printf "\$?=%d " $e     ;;
    esac
  fi
}

ps1_jobs() {
  local count=$1
  if [ $count -gt 0 ]; then
    printf "jobs=%d " ${count}
  fi
}

ps1_git() {
  if jartps1_gitbranch_find; then
    printf "%s " "${jartps1_gitbranch}"
  fi
}

ps1_dir() {
  local path="$PWD"
  case "${path}" in
    ${HOME})
      path="~"
      ;;
    ${HOME}/*)
      path="~/${path#$HOME/}"
      ;;
  esac
  printf "%s" "${path}"
}

if [ -n "${BASH_VERSION}" ]; then
  case ${JARTPS1_THEME:-default} in
    default)
      PS1="\[\e[1;31m\]\$(ps1_error)\[\e[34m\]\$(ps1_jobs \j)\[\e[32m\]\$(ps1_git)\[\e[0;95m\]\u@\h\[\e[m\]:\$(ps1_dir)\$ "
      PS2='> '
      PS4='+ '
      ;;
    dark)
      PS1="\[\e[1;31m\]\$(ps1_error)\[\e[34m\]\$(ps1_jobs \j)\[\e[32m\]\$(ps1_git)\[\e[0;95m\]\u@\h\[\e[m\]:\[\e[0;96m\]\$(ps1_dir)\[\e[0m\]\$ "
      PS2='> '
      PS4='+ '
      ;;
    *)
      printf "Invalid \$JARTPS1_THEME: %s\n" "${JARTPS1_THEME}" >&2
      ;;
  esac
else
  PS1="\$(ps1_error)\$(ps1_git)\$USER@$(hostname -s):\$(ps1_dir)\$ "
  PS2='> '
  PS4='+ '
fi

# Caches last directory for which `jartps1_gitdir_find` failed.
export JARTPS1_GITDIR_TMP="$(mktemp /tmp/jartps1.XXXXXX)"

################################################################################
# Swiftly determine name of current Git branch.
#
# Arguments:
#   None
# Returns:
#   0 on success, storing result to ${jartps1_gitbranch}.
#   1 if ${PWD} isn't inside a Git repo.
# Globals:
#   jartps1_gitbranch      - Used to store result.
################################################################################
jartps1_gitbranch_find() {
  if jartps1_gitdir_find; then
    local head
    if read head <"${jartps1_gitdir}/.git/HEAD" >/dev/null 2>&1; then
      jartps1_gitbranch="${head##*/}"
      if [ x"${jartps1_gitbranch}" != x"" ]; then
        return 0
      fi
    fi
  fi
  return 1
}

################################################################################
# Swiftly locate root of current Git repository.
#
# This is the fastest possible solution. Rather than the naïve approach of
# executing the git command (which could take hundreds of milliseconds), this
# routine launches no processes and only requires a few stat() system calls. In
# some cases it can avoid lookup or cache the result.
#
# Arguments:
#   dir                 - Optional, defaults to ${PWD}
# Returns:
#   0 on success, storing result to ${jartps1_gitdir}.
#   1 if dir isn't inside a Git repo.
# Globals:
#   jartps1_gitdir      - Used to store result.
#   JARTPS1_GITDIR_TMP  - Temp file used to cache last failed search.
################################################################################
jartps1_gitdir_find() {
  local dir="$1"
  if [ -z "${dir}" ]; then
    dir="${PWD}"
    case "${dir}" in
      /)                        return 1 ;;
      ${HOME})                  return 1 ;;
      /google/*)                return 1 ;;
      /home/build/*)            return 1 ;;
      /usr/local/google${HOME}) return 1 ;;
    esac
    if [ -f "${JARTPS1_GITDIR_TMP}" ]; then
      local notgit
      if read notgit <"${JARTPS1_GITDIR_TMP}" >/dev/null 2>&1; then
        if [ "${dir}" == "${notgit}" ]; then
          return 1
        fi
      fi
    fi
  fi
  if [ -d "${dir}/.git" ]; then
    jartps1_gitdir="${dir}"
  else
    local parent="${dir%/*}"
    if [ -z "${parent}" ]; then
      printf "%s" "$PWD" >"${JARTPS1_GITDIR_TMP}"
      return 1
    fi
    jartps1_gitdir_find "${parent}"
  fi
}