Hello again mao9856,
Can you cat -A 4_os_10.txt, I would like to see all the characters format of your file. It looks it is not matching the sample of DATA that you provide us. Also try to use as @ARGV a few files, for example 4_os_10.txt and 4_os_11.txt if you know that they contain even a single line in common.
Also there is a great answer Re: find common data in multiple files from fellow Monk BillKSmith that is using the module setop and it is simplified a lot. Sample of code on how to run the script Re^2: find common data in multiple files.
Give it a try and let us know for both cases, BR.
Seeking for Perl wisdom...on the process of learning...not there...yet!