function extract ()  
{
    if [ -f $1 ] ; then
      case $1 in
        *.tar.bz2)   tar xjf "$1"     ;;  
        *.tar.gz)    tar xzf "$1"     ;;  
        *.bz2)       bunzip2 "$1"     ;;  
        *.rar)       unrar e "$1"     ;;  
        *.gz)        gunzip "$1"      ;;  
        *.tar)       tar xf "$1"      ;;  
        *.tbz2)      tar xjf "$1"     ;;  
        *.tgz)       tar xzf "$1"     ;;  
        *.zip)       unzip "$1"       ;;  
        *.Z)         uncompress "$1"  ;;  
        *.7z)        7z x "$1"        ;;  
        *)     echo "'$1' cannot be extracted via extract()" ;;
         esac
     else
         echo "'$1' is not a valid file"
     fi  
}