Sometimes, the easy solution is to not use perl.

$ find a/b -maxdepth 1 '!' -name '*.zip' -type f -exec rm '{}' ';'
[download]

Or, from Perl:

unlink `find a/b -maxdepth 1 '!' -name '*.zip' -type f`;
[download]

If you're silly enough to put newlines in your filenames, use

unlink split /\x00/, `find a/b -maxdepth 1 '!' -name '*.zip' -type f -
+print0`;
[download]