$ perl pm_11103133.pl <xy.data
CURRENT LINE: <Hello, I'm 18
>
NUMBERS FOUND IN LINE: 18
LARGEST IS: 18
Hello, I'm 18

CURRENT LINE: <1 this year is 2019 1
>
NUMBERS FOUND IN LINE: 1, 1, 2019
LARGEST IS: 1
CURRENT LINE: <1 2 3 - 4
>
NUMBERS FOUND IN LINE: 1, 2, 3, 4
LARGEST IS: 1
CURRENT LINE: <
>
NUMBERS FOUND IN LINE:
Use of uninitialized value $largest_number[0] in concatenation (.) or string at pm_11103133.pl line 14, <STDIN> line 4.
LARGEST IS:
Use of uninitialized value in numeric gt (>) at pm_11103133.pl line 16, <STDIN> line 4.