How to retrieve the full path where a script resides

selfbase.sh

#!/bin/bash
set -o nounset
set -o errexit

selfbase() {
    local selfbase=""
    if [ -f $0 -a ! -h $0 ]; then
        selfbase="$(dirname $0)"
    elif [ $(uname) = "Darwin" ]; then
        selfbase="$(dirname $(readlink $0))"
    else
        selfbase="$(dirname $(readlink -f $0))"
    fi

    if [ $selfbase = "." ]; then
        selfbase=$(pwd)
    fi

    echo $selfbase
}