Improve _is_sourced check

Author: yosifkit

docker-entrypoint.sh

@@ -27,7 +27,9 @@ file_env() {
 # check to see if this file is being run or sourced from another script
 _is_sourced() {
 	# https://unix.stackexchange.com/a/215279
-	[ "${FUNCNAME[${#FUNCNAME[@]} - 1]}" == 'source' ]
+	[ "${#FUNCNAME[@]}" -ge 2 ] \
+		&& [ "${FUNCNAME[0]}" = '_is_sourced' ] \
+		&& [ "${FUNCNAME[1]}" = 'source' ]
 }
 
 # used to create initial posgres directories and if run as root, ensure ownership to the "postgres" user