oh-my-zsh/tools/check_for_upgrade.sh

# Migrate .zsh-update file to $ZSH_CACHE_DIR
if [[ -f ~/.zsh-update && ! -f "${ZSH_CACHE_DIR}/.zsh-update" ]]; then
  mv ~/.zsh-update "${ZSH_CACHE_DIR}/.zsh-update"
fi

# Cancel update if:
# - the automatic update is disabled.
# - the current user doesn't have write permissions nor owns the $ZSH directory.
# - git is unavailable on the system.
if [[ "$DISABLE_AUTO_UPDATE" = true ]] \
   || [[ ! -w "$ZSH" || ! -O "$ZSH" ]] \
   || ! command -v git &>/dev/null; then
  return
fi


function current_epoch() {
  zmodload zsh/datetime
  echo $(( EPOCHSECONDS / 60 / 60 / 24 ))
}

function update_last_updated_file() {
  echo "LAST_EPOCH=$(current_epoch)" >! "${ZSH_CACHE_DIR}/.zsh-update"
}

function update_ohmyzsh() {
  if ZSH="$ZSH" zsh -f "$ZSH/tools/upgrade.sh" --interactive; then
    update_last_updated_file
  fi
}

() {
  emulate -L zsh

  local epoch_target mtime option LAST_EPOCH

  # Remove lock directory if older than a day
  zmodload zsh/datetime
  zmodload -F zsh/stat b:zstat
  if mtime=$(zstat +mtime "$ZSH/log/update.lock" 2>/dev/null); then
    if (( (mtime + 3600 * 24) < EPOCHSECONDS )); then
      command rm -rf "$ZSH/log/update.lock"
    fi
  fi

  # Check for lock directory
  if ! command mkdir "$ZSH/log/update.lock" 2>/dev/null; then
    return
  fi

  # Remove lock directory on exit. `return $ret` is important for when trapping a SIGINT:
  #  The return status from the function is handled specially. If it is zero, the signal is
  #  assumed to have been handled, and execution continues normally. Otherwise, the shell
  #  will behave as interrupted except that the return status of the trap is retained.
  #  This means that for a CTRL+C, the trap needs to return the same exit status so that
  #  the shell actually exits what it's running.
  trap "
    ret=\$?
    unset -f current_epoch update_last_updated_file update_ohmyzsh 2>/dev/null
    command rm -rf '$ZSH/log/update.lock'
    return \$ret
  " EXIT INT QUIT

  # Create or update .zsh-update file if missing or malformed
  if ! source "${ZSH_CACHE_DIR}/.zsh-update" 2>/dev/null || [[ -z "$LAST_EPOCH" ]]; then
    update_last_updated_file
    return
  fi

  # Number of days before trying to update again
  epoch_target=${UPDATE_ZSH_DAYS:-13}
  # Test if enough time has passed until the next update
  if (( ( $(current_epoch) - $LAST_EPOCH ) < $epoch_target )); then
    return
  fi

  # Ask for confirmation before updating unless disabled
  if [[ "$DISABLE_UPDATE_PROMPT" = true ]]; then
    update_ohmyzsh
  else
    # input sink to swallow all characters typed before the prompt
    # and add a newline if there wasn't one after characters typed
    while read -t -k 1 option; do true; done
    [[ "$option" != ($'\n'|"") ]] && echo

    echo -n "[oh-my-zsh] Would you like to update? [Y/n] "
    read -r -k 1 option
    [[ "$option" != $'\n' ]] && echo
    case "$option" in
      [yY$'\n']) update_ohmyzsh ;;
      [nN]) update_last_updated_file ;;
    esac
  fi
}