pasted from http://iohq.net/index.php?title=Finding_the_Absolute_Path_of_a_Bash_Script

getScriptAbsolutePath

#
# Determines the absolute path to the running script. This is useful for
# needing to muck around in the running directory when the script has been
# called using a relative path
#
getScriptAbsolutePath() {
        if [[ ${0:0:1} == '/' ]]; then
                # If the script was called absolutely
                absPath=${0}
        else
                # If the script was called relatively, strip the . off the front
                script=`echo ${0} | sed 's/\.\?\(.*\)$/\1/'`
                absPath="$(pwd)/${script}"
        fi
        # Strip the script filename off the end
        absPath=`echo ${absPath} | sed 's/\(.*\/\).*\$/\1/'`
}