perl - Skipping error in eval{} statement

Question

I am trying to extract data from website using Perl API. I am using a list of URIs to get the data from the website.

Initially the problem was that if there was no data available for the URI it would die and I wanted it to skip that particular URI and go to the next available URI. I used next unless ....; to come over this problem.

Now the problem is I am trying to extract specific data from the web by calling a specific method (called as identifiers()) from the API. Now the data is available for the URI but the specific data (the identifiers), what I am looking for, is not available and it dies.

I tried to use eval{} like this

eval {
    for $bar ($foo->identifiers()){
        #do something
    };
}

When I use eval{} I think it skips the error and moves ahead but I am not sure. Because the error it gives is Invalid content type in response:text/plain.

Whereas I checked the URI manually, though it doesn't have the identifiers it has rest of the data. I want this to skip and move to next URI. How can I do that?

Answer 1

OK, I think I understand your question, but a little more code would have helped, as would specifying which Perl API -- not that it seems to matter to the answer, but it is a big part of your question. Having said that, the problem seems very simple.

When Perl hits an error, like most languages, it runs out through the calling contexts in order until it finds a place where it can handle the error. Perl's most basic error handling is eval{} (but I'd use Try::Tiny if you can, as it is then clearer that you're doing error handling instead of some of the other strange things eval can do).

Anyway, when Perl hits eval{}, the whole of eval{} exits, and $& is set to the error. So, having the eval{} outside the loop means errors will leave the loop. If you put the eval{} inside the loop, when an error occurs, eval{} will exit, but you will carry on to the next iteration. It's that simple.

I also detect signs that maybe you're not using use strict; and use warnings;. Please do, as they help you find many bugs quicker.