Tip #1 from the Basic debugging checklist: use diagnostics:

    (F) You've said "use strict" or "use strict vars", which indicates
+ 
    that all variables must either be lexically scoped (using "my" or 
+"state"), 
    declared beforehand using "our", or explicitly qualified to say 
    which package the global variable is in (using "::").
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Declare all variables with my:

use strict;
use warnings;

my $char = chr(0x394);
my $code = ord($char);

printf "char %s is code %d, %#04x\n", $char, $code, $code;
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See also: perlintro

UPDATE: Geez, this problem was solved for you a month ago :(