Catch warning from external module

p4luch has asked for the wisdom of the Perl Monks concerning the following question:

Hello, I'm quite new to programming in Perl and need help. I have script which downloads data from web server through function from external module. In case of errors (like 500 read timeout) function generates warning. Is it possible to catch this warning in my main script? I've tried to use eval{} on function call but it didn't seem to work. Sorry for not specyfing. I'm using BioMart Perl API to download data from EnsEMBL BioMart mirror. And code for function which downloads data by default isn't avaible for user. Piece of code which generetes warning looks like that:

        my $ua = LWP::UserAgent->new;
    $ua->timeout(20); # default is 180 seconds
    $ua->proxy( ['http', 'https'], $self->proxy ) if defined $self->pr
+oxy;
    my $response = $ua->request($request);
    
    my @results;
    
    if ($response->is_success) {
    my @arr=split(/\n/,$response->content); # much neater to use 'cont
+ent' instead of 'as_string', we don't need to explicitly ignore heade
+r part of the http response any more.
    foreach my $el(@arr){         
        $logger->warn("RESPONSE:  $el");
        push (@results,$el);
    }
    
    }  else {
    warn ("\n\nProblems with the web server: ".
          $response->status_line."\n\n");
    }
[download]

And I'm intrested "catching" warning from last warn().But I have to do it in my main script.

Comment on Catch warning from external module Download Code

Replies are listed 'Best First'.

Re: Catch warning from external module
by marto (Cardinal) on Jul 18, 2014 at 08:47 UTC

Which module are you using? Many modules provide the ability to check for status. It would be easier for people to provide sound advice if you show an short example which illustrates your problem. See also How do I post a question effectively? and PerlMonks for the Absolute Beginner.

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Re^2: Catch warning from external module

by tbone654 (Beadle) on Jul 19, 2014 at 03:41 UTC

Put this at the very beginning of your code before anything else

BEGIN {
    $| = 1;
    open (STDERR, ">&STDOUT");
    print qq~Content-type: text/html\n\n~;
}
[download]

[reply]
[d/l]

Re: Catch warning from external module
by Anonymous Monk on Jul 18, 2014 at 08:50 UTC

I've tried to use eval{} on function call but it didn't seem to work.

What does the documentation say, how are you supposed to tell when this function fails, and how are you supposed to tell why it fails (an error variable/attribute/method)?

Yes, you can trap warnings in perl, but its not as convenient as eval


local $SIG{__WARN__} = \&catch_warnings;
emit_some_warnings();

# catch_warnings($msg)
sub catch_warnings {
    my( $msg ) = @_;
    print "I caught this warning $msg\n";
}
[download]

Whatever this external module is, you should study its documentation :)

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Re: Catch warning from external module
by Athanasius (Archbishop) on Jul 18, 2014 at 16:00 UTC

Hello p4luch, and welcome to the Monastery!

Since warn prints to STDERR, you may find it sufficient to simply catch any output to STDERR and use that. For this purpose, the module Capture::Tiny provides a subroutine called capture_stderr:


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