If you can't figure out what a warning/error means, employ

    use diagnostics;
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in your code or call perldoc perldiag on the command line:

Character in "c" format wrapped in pack
(W pack) You said

   pack("c", $x)

where $x is either less than -128 or more than 127; the
"c" format is only for encoding native operating system
characters (ASCII, EBCDIC, and so on) and not for
Unicode characters, so Perl behaved as if you meant

   pack("c", $x & 255);

If you actually want to pack Unicode codepoints, use 
the "U" format instead.
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