To elaborate a bit on FunkyMonk's response, the period (.), when used in regular expressions means "any character except¹ the newline." The way split is to break a string into fields, throwing out the specified separator², which is a regular expression. When I try splitting a string with /./, I get an empty array.

If you want to split a string on periods (.), you've got to escape it, with the backslash (\), so your split should look something like this:

@file = split(/\./, $file_name);
[download]

(which is exactly what FunkyMonk wrote).

Regex are fun, and an incredibly powerful part of Perl.

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1: Usually.

2: Although you can keep it if you want, by surrounding the regex with parentheses.