set_value (hash_key: string, key_value: string) : nil
    get_value (hash_key: string) : string

##</code><code>##

$code = <<DONE;
sub func {
    print "hello, world.\n";
}
DONE

eval $code;
&func;

##</code><code>##

$file = '/some/file/path';
open (CODE, $file) or die qq(can't read "$file": $!);

$tmp = $/ ; undef $/;
$code = <CODE>;
$/ = $tmp;

close CODE;

eval $code;

##  and then run some function defined in that code.