source_location=$(find $SOURCE -regextype posix-extended -regex "$FILTER_REGEX")

.*/$key_[0-9]{4}-[0-9]{2}-[0-9]{2}-[0-9]{2}.[0-9]{2}.[0-9]{2}.txt

example_2014-12-31-23.59.59.txt
example_actvy_log_2014-12-31-23.59.59.txt
example_actvy_log_2015-12-31-23.59.59.txt
example_my_file_2012-12-31-23.59.59.txt