The question is, how are you running the program?

Most likely, you're running the program from the command line without naming any files to be altered, or you're running it under Windows, with only giving a wildcard match to the script. In both cases, you can give or expand the script files to be matched by prepopulating the @ARGV array:

...
use strict;
use File::Glob qw(bsd_glob);

@ARGV = glob '*.pl'; # to treat all .pl files

...
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