The consequent of using strict is that you must either 'declare' variables with my or our, or use a fully qualified package name (see strict vars). The above code can be repaired with

#!/usr/bin/perl
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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