catching warnings

Anarion has asked for the wisdom of the Perl Monks concerning the following question:

I try to catch into a variable this warning:

Useless use of a variable in void context
[download]

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
[download]

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

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

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

Comment on catching warnings Select or Download Code

Replies are listed 'Best First'.
Re: catching warnings by jsprat (Curate) on Apr 26, 2002 at 01:59 UTC
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');` [download] Note: any of the categories of warnings will work. Good luck!	[reply] [d/l] [select]
Re: catching warnings by Fletch (Bishop) on Apr 26, 2002 at 01:51 UTC
For recent perls (5.6 or newer): `no warnings 'void';`. See perllexwarn and warnings.	[reply] [d/l]
Re: Re: catching warnings by Anarion (Hermit) on Apr 26, 2002 at 10:00 UTC
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	[reply]