This is what I would expect an example program to look like:

#!/usr/bin/perl

use strict;
use warnings;

print 'A';        # Prints 'A'

print chr(65);    # Prints 'A'

my $c = 65;
print chr($c);    # Prints 'A'

$_ = 65;
print chr;        # Prints 'A'
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I'll assume that you've successfully tested that on your system; however, consider:

• Not all systems have /usr/bin/perl.
• chr() does not require the strict pragma.
• chr() works on versions of Perl5 prior to the introduction of the warnings pragma.
• A variable, supplied as an argument to chr(), does not need to be lexical.

So, as you can probably see, there's no one-size-fits-all example. Providing explanations and code fragments is likely to be suitable for a wider audience; even then, many pages require links to perlport or other caveats.

"I will study the GitHub link ... although it's quite messy."

Well, I didn't have any trouble finding the chr() tests for the latest stable release, https://github.com/Perl/perl5/blob/v5.36.1/t/op/chr.t, or those from over a decade ago, https://github.com/Perl/perl5/blob/v5.16.0/t/op/chr.t.

At the end of the day, if you're really struggling with using some function, ask here: we're always happy to help. I would request that you restrict your questions to a single function or related group of functions; listing every operator and function that you can find is just off-putting — many who could otherwise provide insightful responses may simply move on to the next question.