These lines:

use Encode;
$str = decode_utf8("ab\x{cc}");
$str =~ s/(\P{PosixPrint})/sprintf("U+%04X", $1)/eg;
print "$str\n";

output abU+0000. Why does the Unicode character comes out as zero in the back reference? I get the same zero result with other Posix* properties, with \p as well as \P (mutatis mutandis), etc.

I also tried without the decode_utf8; no difference. (Sorry, I've never understood when it's needed and when it's not, so I just tried both ways.)

Also no difference with use feature 'unicode_strings'; (which I don't want in my real program, anyway).

I know there are other ways to accomplish the job being done here, of converting binary Unicode characters into ASCII representations, e.g., encode("ascii", decode_utf8($str), Encode::FB_XMLCREF), the nice_string function from perluniintro, etc. I'm wondering here about the regexp usage in particular.

This is with perl 5.30.2 on CentOS Linux; I built the binary from the original source, no distro packaging involved.

I feel sure I'm missing something obvious, but I can't find the answer in either the myriad perluni* docs or on the net. Apologies and thanks in advance.

In reply to \P{PosixPrint} back reference? by karlberry

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