Shell script best practices, from a decade of scripting things(sharats.me)

    if [[ "$1" =~ ^-*h(elp)?$ ]]; ...

    if [[ "${1-}" =~ ^-*h(elp)?$ ]]; then

    [ "${some_var-}" ] && do_something

    f(){ [ "${some_var-}" ] && do_something;}; f

    if [[ "${TRACE-0}" == "1" ]]; then set -o xtrace; fi

  while getopts :hvr:e: opt
  do
      case $opt in
          v)
              verbose=true
              ;;
          e)
              option_e="$OPTARG"
              ;;
          r)
              option_r="$option_r $OPTARG"
              ;;
          h)
              usage
              exit 1
              ;;
          \*)
              echo "Invalid option: -$OPTARG" >&2
              usage # call some echos to display docs or something...
              exit 2
              ;;
      esac
  done

  LINE_COUNT=0
  some command | while read -r X
  do
    # This runs in a sub-shell; it inherits the initial LINE_COUNT from the parent,
    # but any mutations are limited to the sub-shell, will be discarded
    (( LINE_COUNT++ ))
  done
  echo "$LINE_COUNT"  # This will echo '0', since the incremented version was discarded

  LINE_COUNT=0
  while read -r X
  do
    # This runs in the main shell; its increments will remain afterwards
    (( LINE_COUNT++ ))
  done < <(some command)
  echo "$LINE_COUNT"  # This will echo the number of lines outputted by 'some command'

  def sh(script):
    subprocess.run(
      [‘sh’, ‘-c’, script, ‘--‘, *args],
      check=True,
    )

  https://github.com/HenrikBengtsson/shellcheck-repl  

  grep -q thing < file
  if [ $? -eq 0 ] ; then echo "thing is there ; fi
  

  if
    grep -q thing < file
  then
    echo "thing is there"
  fi

    export PS4='+ ${BASH_SOURCE:-}:${FUNCNAME[0]:-}:L${LINENO:-}:   '

    echo_command()
    {
        echo
        echo '$' "$@"
    }

    echo_and_run_command()
    {
        echo_cmd "$@"
        "$@"
    }

    main()
    {
        # For simple commands that do not use | < > etc.
        echo_and_run_command cp --verbose ...

        # More complex commands
        echo_command grep ... '|' find ...
        grep ... | find ...
    }

    main "$@"