Source without circular reference 

[ ! "${LIB}" ] && ( readonly LIB; . "${ $( cd $( dirname $0 ) && pwd ) }/<path_to>/LIB.sh" )

January 24, 2018 — dhsrocha

Explanation

Source LIB only if the corresponding variable is not defined, in order to prevent circular reference loop in case of the same script has been sourced before during the sourcing event.

script-sourcing circular-reference
cd pwd dirname readonly