Re: command for swapping of two files or two dirs?

[Greg Wooledge]

On Fri, Mar 26, 2021 at 11:28:15PM +0100, Alex fxmbsw7 Ratchev wrote:
> swap_maybe_safer() { declare t=
>  while [[ -e ${t:=.$SRANDOM$SRANDOM}.} ]] &&  t= ; do :; done
> 
> cp -p "$1" "$t"
> mv "$2" "$1"
> mv "$t" "$2"
> }

This is so sad.  I can't take it any more.

# swap_files file1 file2
# Exit status:
#  0 success
#  1 user error
#  2 runtime error occurred, no side effects
#  3 runtime error occurred, with side effects
swap_files() {
  if (($# != 2)); then
    printf 'usage: swap_files file1 file2\nFiles must be in the same dir\n' >&2
    return 1
  fi

  local dir dir2 temp i=0

  case $1 in
    */*) dir=${1%/*} ;;
    *)   dir=. ;;
  esac
  case $2 in
    */*) dir2=${2%/*} ;;
    *)   dir2=. ;;
  esac

  if [[ $dir2 != $dir ]]; then
    echo 'Files must be in the same dir' >&2
    return 1
  fi

  while ((++i < 100)); do
    temp=$dir/.$$.$RANDOM
    [[ -e $temp ]] && continue
    ln -- "$1" "$temp" || return 2
    if ! mv -- "$2" "$1"; then
      rm -- "$temp"
      return 2
    fi
    if ! mv -- "$temp" "$2"; then
      echo 'The first move succeeded, but the second failed.  HELP!' >&2
      return 3
    fi
    return 0
  done

  echo 'Could not find an unused temp file name' >&2
  return 2
}