extract () {
  [ ! "$1" ]    && { echo "usage: extract [file]"; return 0; }
  [ ! -f "$1" ] && { echo "$1 is not a file!";     return 1; }

  case "$1" in
      *.tar.bz2)   tar xvjf   "$1" || return $? ;;
      *.tar.gz)    tar xvzf   "$1" || return $? ;;
      *.bz2)       bunzip2    "$1" || return $? ;;
      *.rar)       rar x      "$1" || return $? ;;
      *.gz)        gunzip     "$1" || return $? ;;
      *.tar)       tar xvf    "$1" || return $? ;;
      *.tbz2)      tar xvjf   "$1" || return $? ;;
      *.tgz)       tar xvzf   "$1" || return $? ;;
      *.zip)       unzip      "$1" || return $? ;;
      *.Z)         uncompress "$1" || return $? ;;
      *.7z)        7z x       "$1" || return $? ;;
      *)           echo "$1 is not of a known archive type"; return 1 ;;
  esac
}