alias cd.='pwd'
alias cd..='cd ..'
alias cd,,='cd ..'
alias ..='cd ..'
alias ,,='cd ..'
alias ...='cd ../..'
alias up2='cd ../..'
alias up3='cd ../../..'
alias up4='cd ../../../..'
# useage up 3 cd ../../..
up(){
  local d=""
  limit=$1
  for ((i=1 ; i <= limit ; i++))
    do
      d=$d/..
    done
  d=$(echo $d | sed 's/^\///')
  if [ -z "$d" ]; then
    d=..
  fi
  cd $d
}