A regex pattern that worked in 5.8 will also work in 5.10. What did you have in 5.8?
'^(\S+)\s+(\S+)\s+(\S+)\s+\[([^\]]*)\]\s+\1\z'
Well, that will continue to work in 5.10. If you wanted to use named captures,
'^(?<fname>\S+)\s+(?<mname>\S+)\s+(?<lname>\S+)\s+\[(?<date>[^\]]*)\]\
+s+\k<fname>\z'
PS — Make sure to test your code with the following string:
"Test Tester Testing [Feb 18: 28_10_10] Tests"
It shouldn't match ("Test" ne "Tests"), but it's easy to match it if the pattern isn't properly anchored.