$ cat posix.pl 
#!/usr/bin/env perl 
use strict;
use warnings;

my $str = "ab\x{cc}";
$str =~ s/(\P{PosixPrint})/sprintf("U+%04X", $1)/eg;
print "$str\n";
$ ./posix.pl 
Argument "Ì" isn't numeric in sprintf at ./posix.pl line 6.
abU+0000
$