pushpop

linux脚本编程的例子

getNdirs ()
{
    stackfront=''
    let count=0
    while [ $count -le $1 ]; do
        target=${DIR_STACK%${DIR_STACK#* }}
        stackfront="$stackfront$target"
        DIR_STACK=${DIR_STACK#$target}
        let count=count+1
    done

    stackfront=${stackfront%$target}
}

pushd ()
{
    if [ $(echo $1 | grep '^+[0-9][0-9]*$') ]; then

        # case of pushd +n: rotate n-th directory to top
        let num=${1#+}
        getNdirs $num

        DIR_STACK="$target$stackfront$DIR_STACK"
        cd $target
        echo "$DIR_STACK"

    elif [ -z "$1" ]; then
        # case of pushd without args; swap top two directories
        firstdir=${DIR_STACK%% *}
        DIR_STACK=${DIR_STACK#* }
        seconddir=${DIR_STACK%% *}
        DIR_STACK=${DIR_STACK#* }
        DIR_STACK="$seconddir $firstdir $DIR_STACK"
        cd $seconddir

    else
        # normal case of pushd dirname
        dirname=$1
        if [ \( -d $dirname \) -a \( -x $dirname \) ]; then
            DIR_STACK="$dirname ${DIR_STACK:-$PWD" "}"
            cd $dirname
            echo "$DIR_STACK"
        else
            echo still in "$PWD."
        fi
    fi
}

popd ()
{
    if [ $(echo $1 | grep '^+[0-9][0-9]*$') ]; then

        # case of popd +n: delete n-th directory from stack
        let num=${1#+}
        getNdirs $num
        DIR_STACK="$stackfront$DIR_STACK"
        cd ${DIR_STACK%% *}
        echo "$PWD"

    else

        # normal case of popd without argument
        if [ -n "$DIR_STACK" ]; then
            DIR_STACK=${DIR_STACK#* }
            cd ${DIR_STACK%% *}
            echo "$PWD"
        else
            echo "stack empty, still in $PWD."
        fi
    fi
}