catching warnings

[Anarion]

I try to catch into a variable this warning:

Useless use of a variable in void context

I have tried to trap it with $SIG{__WARN__} but it doesn't work outside of a BEGIN block, and that's what I want. Here's some code:

lorien:~$ perl -wle '$SIG{__WARN__}=sub{print"TRAPED"};s///'
TRAPED
TRAPED
lorien:~$  perl -wle '$SIG{__WARN__}=sub{print"TRAPED"};$.,$.=0'
Useless use of a variable in void context at -e line 1.
lorien:~$  perl -wle 'BEGIN{$SIG{__WARN__}=sub{print"TRAPED"};}$.,$.=0
+'
TRAPED

I have tried to use it inside an eval block:

lorien:~$  perl -wle '$SIG{__WARN__}=sub{print"TRAPED"};eval q{$.,$.=0
+;}'
lorien:~$
lorien:~$  perl -wle '$SIG{__WARN__}=sub{print"TRAPED"};eval {$.,$.=0;
+}'
Useless use of a variable in void context at -e line 1.
lorien:~$

Any idea of why that happens and how to catch it without a BEGIN block?
$anarion=\$anarion;

s==q^QBY_^=,$_^=$[x7,print

[Fletch]

For recent perls (5.6 or newer): no warnings 'void';. See perllexwarn and warnings.

[Anarion]

I already checked that before post.

I don't want to ignore warnings, I want to save it into a variable, but without the begin i can't.

$anarion=\$anarion;

s==q^QBY_^=,$_^=$[x7,print

[jsprat]

Do you want to execute something when the warning occurs or do you just want to swallow it? If you want it to disappear, then

no warnings qw(void);

should do the trick. If you want to print a custom message, try

warnings::warn('void', 'TRAPED');

Note: any of the categories of warnings will work.
Good luck!