direnv disabler script, inspired by "basher" uninstall script

disable_direnv.sh

#!/usr/bin/env bash
## direnv disabler script, inspired by "basher" uninstall script
# shellcheck disable=SC2034

die() {
  echo "!! $1 " >&2
  echo "!! -----------------------------" >&2
  exit 1
}

## stop if direnv is not installed
command -v direnv >/dev/null 2>&1 || die "I require direnv but it's not installed.  Aborting."

## now check what shell is running
shell_type=$(basename "$SHELL")
echo ". detected shell type: $shell_type"
case "$shell_type" in
bash)  startup_type="simple" ; startup_script="$HOME/.bashrc" ;;
zsh)   startup_type="simple" ; startup_script="$HOME/.zshrc"  ;;
sh)    startup_type="simple" ; startup_script="$HOME/.profile";;
fish)  startup_type="fish"   ; startup_script="$HOME/.config/fish/config.fish"  ;;
*)     startup_type="?"      ; startup_script="" ;   ;;
esac

## startup script should exist already
[[ -n "$startup_script" && ! -f "$startup_script" ]] && die "startup script [$startup_script] does not exist"

## direnv_keyword will allow us to remove the lines upon uninstall
direnv_keyword="direnv5ea843"

if grep -q "$direnv_keyword" "$startup_script" ; then
  echo ". remove direnv from startup script [$startup_script]"
  sleep 1
  temp_file="$startup_script.temp"
  cp "$startup_script" "$temp_file"
  < "$temp_file" grep -v "$direnv_keyword" > "$startup_script"
  rm "$temp_file"
elif grep -q direnv "$startup_script" ; then
    grep direnv "$startup_script"
    die "Can't auto-remove the lines from $(basename $startup_script) - please do so manually "
else
    die "Can't find initialisation commands for direnv"
fi

## script is finished
echo "direnv config is uninstalled"