Especially if you are a beginner, you should place the statements  use warnings; and  use strict; at the beginning of all your code:

c:\@Work\Perl\monks>perl -le
"use warnings;
 use strict;
 ;;
 use utf8;
 ;;
 my $pi_char = chr(OxO3c9);
 print qq{Greek letter '$pi_char' here};
"
Bareword "OxO3c9" not allowed while "strict subs" in use at -e line 1.
Execution of -e aborted due to compilation errors.
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I.e., "OxO3c9" (letter "O" vice decimal digit "0") is not a hex number, as already noted. See warnings and strict.

In other words, "Help Perl to help you."