I tried this code using it as follow:

$ perl test.pl *.txt
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And it is giving output:

$VAR1 = [];
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Are you running the script in the directory containing the *.txt files?

What operating system are you using? If you are on Windows, there are some minor differences to Unix that prevent *.txt from being expanded to a list of files. In that case, add the following line to the perl script, right after "use warnings;":

use Win32::Autoglob;
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(See Re^3: Perl Rename for details why this is needed.)

Alexander