The things I was mostly looking forward to were state, the builtin switch statement, the // operator and say.

However, today I very happily discovered that Perl 5.10 eliminates my previously number one complaint about error messages.

A colleague asked me today whether I knew of a way to find which variable was undefined in a line containing a string composed of many variables.  On the off-chance that this was better handled in 5.10 (which I hadn't yet read about), I tried a sample program in Perl 5.10, and was pleasantly surprised to find that:

use strict;
use warnings;

my $a = 1;
my $b = 1;
my $c = 1;
my $d;
my $e = 1;
my $f = 1;
my $g = 1;
my $h = 1;

print "$a$b$c$d$e$f$g$h\n";
[download]

Run this with Perl 5.8.0 and you get:

    
Use of uninitialized value in concatenation (.) or string at x.pl line
+ 14.
1111111
[download]

Whereas with Perl 5.10.0:

    
Use of uninitialized value $d in concatenation (.) or string at x.pl l
+ine 14.
1111111
[download]

It's a minor textual difference, but a huge difference diagnostically!

I'm very happy to upgrade to Perl 5.10!