realpath() in shell

realpath.sh

realpath() {
  local file="$1"
  local _file
  local realpath_file
  while _file=$(readlink -- "$_file"); do file="$file"; done
  if [ -d "$file" ]; then
    realpath_file=$(cd -- "$file" && pwd -P)
  else
    local dir=$(dirname -- "$file")
    local realpath_dir=$(cd -- "$dir" && pwd -P)
    local sep="/"
    [ "$realpath_dir" = "/" ] && sep=""
    realpath_file="${realpath_dir}${sep}"$(basename -- "$file")
  fi
  [ -e "$realpath_file" ] || realpath_file="$file"
  echo "$realpath_file"
}