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

my $i = 10;

sub TIEHANDLE {
    return bless {}, 'main';
}

sub PRINT {
    my ($self, $str) = @_;
    print STDOUT "in PRINT: <<$str>>\n";
}

tie *STDERR, 'main';

warn "foo";
eval {
    $i->foo();
};
__END__
in PRINT: <<foo at test.pl line 18.
>>
[download]

In this case the error from within the eval doesn't get forwarded to PRINT.

Could you please provide an example that we can use to reproduce your error?

That doesn't make sense. Exceptions such as the one you provided are caught by eval and don't print anything.

>perl -we"$a=10; $a->isa('foo');"
Can't call method "isa" without a package or object reference at -e li
+ne 1.

>perl -we"eval { $a=10; $a->isa('foo'); }"

>
[download]

So you either used a bad example or you have a buggy __DIE__ handler. (It should check $^S.)

Assuming you just picked a bad example, eval doesn't affect warnings, which can be avoided with writing a warning handler

>perl -we"eval { $a='abc'; $a += 5; }
Argument "abc" isn't numeric in addition (+) at -e line 1.

>perl -we"eval { local $SIG{__WARN__} = sub {}; $a='abc'; $a += 5 }"

>
[download]

Of course, that neither eval nor a warning handler prevents from writing to STDERR in general. local *STDERR; will handle most cases. The exception would be if you spawned a child process.

>perl -we"eval { print STDERR qq{foo\n}; }"
Argument "abc" isn't numeric in addition (+) at -e line 1.

>perl -we"eval { local *STDERR; print STDERR qq{foo\n}; }"
print() on unopened filehandle STDERR at -e line 1.

>perl -we"eval { local $SIG{__WARN__} = sub {}; local *STDERR; print S
+TDERR qq{foo\n}; }"
print() on unopened filehandle STDERR at -e line 1.

>
[download]

By the way, you can avoid the need for any of shenanigans in this particular case by using isa as a function.

>perl -we"$a=10; UNIVERSAL::isa($a, 'foo');"

>
[download]

By the way, you can avoid the need for any of shenanigans in this particular case by using isa as a function.

... in the same way that you can avoid warnings by not using strict and warnings and redirecting STDERR to /dev/null.

No, turning off warnings will not turn them off in called functions and won't mute explicit calls to warn.

Yes, redirecting STDERR is another option (although /dev doesn't exist on my system).

>perl -we"eval { local *STDERR; open(STDERR, '>', 'NUL'); print STDERR
+ qq{foo\n}; }"

>
[download]

I seem to remember that  caller(0) can give you that information. You have to specify the call-frame explicitly to get the full spectrum of data. The fourth element of the array is 'subroutine name', if you are in an eval block it reads '(eval)'.

$^S is an easier way to check if you're in an eval.

Update: I thought now about a tiny test for this:
perl -e '$a=10; eval { $SIG{__WARN__} = sub {  }; $a->isa('foo')}; print "Eval: ", $@, "\n"'
or
perl -e '$a=10; eval { $SIG{__WARN__} = undef; $a->isa('foo')}; print "Eval: ", $@, "\n"'

Both have the warning still in $@. I can't say much about a tied STDERR but it looks pretty much that this isn't working. One another idea I had was to localise the STDERR typeglob inside eval:

perl -e '$a=10; eval { local *STDERR; print STDERR "Test\n"; $a->isa('foo'); }; print $@;'

While this still sets the warning inside $@ the message to STDERR isn't printed. It's worth a try.

Close, but so wrong!
• $SIG{__WARN__} should have been localized.
• $SIG{__WARN__} doesn't hide the message from an exception such as $a=10; $a->isa('foo').
• local *STDERR; simply replaces the text with the warning "print() on unopened filehandle STDERR".
• Warnings don't set $@.

Aha! Yes, I did redefine the sig handlers for warn and die and that is the problem. I'm not even sure why I did it any more this was written so long ago.

Silly me... thanks!

                - Ant
                - Some of my best work - (1 2 3)