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From WWW::Mechanize:

autocheck => [0|1]

Checks each request made to see if it was successful. This saves you the trouble of manually checking yourself. Any errors found are errors, not warnings.

The default value is ON, unless it's being subclassed, in which case it is OFF. This means that standalone WWW::Mechanizeinstances have autocheck turned on, which is protective for the vast majority of Mech users who don't bother checking the return value of get() and post() and can't figure why their code fails. However, if WWW::Mechanize is subclassed, such as for Test::WWW::Mechanize or Test::WWW::Mechanize::Catalyst, this may not be an appropriate default, so it's off.
Here, errors means die(). Since your program used autocheck=>1 by default, it dies when a problem occurs while calling $mech_cgi->follow_link(...). It has no chance to reach your own call to die - which is not what you want - as already observed by roboticus (Updated: paragraph).

Now you have at least two options:

  • Wrap the calls that can fail into an eval-block and check for exceptions ($@), or
  • create the WWW::Mechanize object using ...new( autocheck=>0 ) and check the results (see HTTP::Response) of $mech_cgi-calls for problems.

Example (2nd alternative):

use strict; use WWW::Mechanize; use Storable; my $mech_cgi = WWW::Mechanize->new( autocheck => 0 ); $mech_cgi->get( 'http://www.molmovdb.org/cgi-bin/browse.cgi' ); my @cgi_links = $mech_cgi->find_all_links( url_regex => qr/motion.cgi/ + ); for my $link ( @cgi_links ) { # no C-style loop... print "following link: ", $link->url, "\n"; my $res = $mech_cgi->follow_link( url => $link->url ); # $res is a HTTP::Response object if ( $res->is_success ) { print "OK : Processing result ...\n"; } else { print "ERR: Failed to retrieve page: ", $res->status_line, "\n"; } $mech_cgi->back; sleep 5; # anti-aggressive scraping }

Result:

... following link: http://www.molmovdb.org/cgi-bin/motion.cgi?ID=ntrc OK : Processing result ... following link: http://www.molmovdb.org/cgi-bin/motion.cgi?ID=ppar ERR: Failed to retrieve page: 500 Internal Server Error following link: http://www.molmovdb.org/cgi-bin/motion.cgi?ID=rhorbp OK : Processing result ... ...

Please check also if you have permission to scrape this site.


In reply to Re: conditional testing for error 500 webpages before following them? by Perlbotics
in thread conditional testing for error 500 webpages before following them? by fraizerangus

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    [Lady_Aleena]: Corion, ouchy.
    [Corion]: (maybe I should write this up as a SoPW) - currently, the "most efficient" data structure I come up with is a single array which I scan for the first fitting one-shot. Not efficient but I don't expect more than five outstanding one-shots anyway
    [choroba]: can't you create a meta-key corresponding to the disjunction of the events?
    [robby_dobby]: Corion: Heh. This whole thing smells of Strategy Pattern or MVC pattern.
    [Corion]: And performance linear to the number of registered one-shots doesn't feel that bad. Maybe I should collect statistics on how many callbacks are outstanding ;)
    [Corion]: choroba: Yes, but the longer I thought about efficient hashes mapping the event type back to their callbacks, and how to keep them in sync, the more I thought that all that optimization might just not be worth it, even if it's horribly inelegant
    [Lady_Aleena]: My biggest problem with hashes at the moment is one with 2,501 keys.
    [choroba]: how many event types are there?
    [Corion]: Also I found that I can't conveniently weaken an array slot, which also is inconvenient, as I want my one-shots to disappear if the caller discards them
    [Corion]: choroba: Currently two or three that my program handles (WWW::Mechanize:: Chrome), but there might be more that become interesting

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