Hi, there is no simple way to do that and the exact behavior as described I can't emulate (today). I believe, that it's possible with deeper knowledge in perlXS, to access the exact codeline which throw the warning and extract their content. But you can define a signalhandler and use PadWalker to print out the lexical and global variables. The following example output these warnings:

Warning: Use of uninitialized value in concatenation (.) or string at mpu.cgi line 25.
Possible variables are:
          '$GLOBAL_VARIABLE' => \'global',
          '$t' => \undef,
          '$s' => \'regular output'

#!/usr/bin/perl
use strict;
use warnings;

use PadWalker();
use Data::Dumper();

local $SIG{'__WARN__'} = sub {
    if($_[0] !~ /^Use of uninitialized value/) {
        print @_;
    } else {
        # If there are objects, the output can be VERY large when you 
+increase this
        local $Data::Dumper::Maxdepth = 2;
        # takes all lexical variables from caller-nemaspace
        my $possibles = Data::Dumper::Dumper({ %{PadWalker::peek_my(1)
+}, %{PadWalker::peek_our(1)} });
        $possibles ne "\$VAR1 = {};\n" ? ($possibles =~ s/^.*?\n(.*)\n
+.*?\n$/$1/ms) : ($possibles = '');
        print STDERR "Warning: " . join(', ', @_) . "Possible variable
+s are:\n$possibles\n";
    }
};

our $GLOBAL_VARIABLE = 'global';
sub mySub {
    my $t = undef;
    my $s = "regular output";
    print " $s $t ";
}
mySub();
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Warnings abouot uninitialized values are resolved, all others behave like before. This you should use only to develop. Some warings about uninitialized variables can be very large, when the caller-namespace contain many variables. Tobiwan