Why doesn't Perl 5 tell you the name of the variable when it complains about uninitialized values?

Why doesn't Perl 5 give me the name of the开发者_运维问答 variable it is complaining about?

perl5.8.9 -we 'my $u; print "$u\n"'
Use of uninitialized value in concatenation (.) or string at -e line 1.

---

It has since version 5.10 which was released in 2007, it is time to upgrade (5.12.2 is coming out shortly).

perl5.10.0 -we 'my $u; print "$u\n"'
Use of uninitialized value $u in concatenation (.) or string at -e line 1.