short_command.sh

# Extract many files with one command
function extract () {
  if [ -f $1 ] ; then
    case $1 in
      *.tar.bz2)   tar xvjf $1    ;;
      *.tar.gz)    tar xvzf $1    ;;
      *.tar.xz)    tar Jxvf $1    ;;
      *.bz2)       bunzip2 $1     ;;
      *.rar)       rar x $1       ;;
      *.gz)        gunzip $1      ;;
      *.tar)       tar xvf $1     ;;
      *.tbz2)      tar xvjf $1    ;;
      *.tgz)       tar xvzf $1    ;;
      *.zip)       unzip -d `echo $1 | sed 's/\(.*\)\.zip/\1/'` $1;;
      *.Z)         uncompress $1  ;;
      *.7z)        7z x $1        ;;
      *)           echo "don't know how to extract '$1'" ;;
    esac
  else
    echo "'$1' is not a valid file!"
  fi
}

# Needn't to cd ../../../ any longer. Just up 3 
function up () {
  LIMIT=$1
  P=$PWD/..
  for ((i=1; i < LIMIT; i++))
  do
    P=$P/..
  done
  cd $P
}