I am attaching you the full code that I am executing.

This code does not compile, so it can't be the code you're running. If I fix the obvious compilation errors, the code seems to work for me. I'm still confused how you're apparently getting undef values for the filenames - perhaps you could insert the line use Data::Dumper; print Dumper([glob '/user/*/ws/*/BLK_*/*.txt']); before the first for loop and show us the output. Otherwise, please see the three links in my previous post.