BASH_SOURCE and FUNCNAME
$BASH_SOURCE only has multiple entries if function calls are involved, in which case its elements parallel the
FUNCNAME array that contains all function names currently on the call stack.
That is, inside a function, ${FUNCNAME[0]} contains the name of the executing function, and ${BASH_SOURCE[0]}
contains the path of the script file in which that function is defined, ${FUNCNAME[1]} contains the name of the function
from which the currently executing function was called, if applicable, and so on.
If a given function was invoked directly from the top-level scope in the script file that defined the function at
level $i of the call stack, ${FUNCNAME[$i+1]} contains:
main (a pseudo function name), if the script file was invoked directly (e.g., ./script)
source (a pseudo function name), if the script file was sourced (e.g. source ./script or . ./script).
Source: StackOverflow