Great! That's an unrelated error that you would need to fix no matter which version of Perl you were using.

You're trying to capturing something, but Perl didn't capture it because it didn't think it needed too. It tries to capture the minimum amount of varaibles.

Note that

try { ... } catch { ... };
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try(sub { ... }, catch(sub { ... }));
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The error occurs with eval EXPR:

$ perl -wle'
    sub f { my $x = "abc"; sub { eval q{"[$x]"} } };
    print f()->();
'
Variable "$x" is not available at (eval 1) line 1.
Use of uninitialized value in print at -e line 1.
[]
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The workaround is to make sure the sub references the lexical variables you will need in the eval EXPR:

$ perl -wle'
    sub f { my $x = "abc"; sub { $x if 0; eval q{"[$x]"} } };
    print f()->();
'
[abc]
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Thanks ikegami but I'm still not quite understanding this but I certainly appreciate your help. In your example you've used $x for the "workaround". I don't understand why I have to do this. Perhaps it would be easier if I posted the exact code (comments labelled MJE I added):

sub queue_job
{
    my ($betdb, $q, $job) = @_;
    my $key;

    $job->{jobid} = new_job_id($betdb);

    # MJE - obviously this can be undef but in the case in
    # question it is usually set
    my $clientref = $job->{clientref} if (exists($job->{clientref}));

    #
    # Insert info about this job in the audit file.
    # NOTE: This will fail if we've seen this client_reference before 
+as
    # client_reference is unique and it would indicate a client has su
+bmitted
    # the same job twice e.g. posted the same job twice.
    #
    my $caught = try {
        my $repost = $clientref ? 0 : undef;

        $betdb->execProc(
            $p_run_or_queue_job,
            {DieOnError => 1, Comment => 'queue_job'},
            $job->{jobid}, $clientref,
            $job->{sessionid}, $job->{name},
            {clob => $json->objToData($job)},
            $repost, 1);
        0;
    } catch {
        my $ev = $_;
        if (($betdb->getDBh())->err == 1) {   # constraint violation
            eval {
                $betdb->callPkgProc(
                    {DieOnError => 1, Comment => 'run_now'},
                    BET::DB::SYN_PKG_BETDB,
                    'p_invalidJobRequest',
                    $job->{jobid},
                    $clientref,
                    $job->{sessionid},
                    $job->{name},
                    $json->objToData($job->{args}),
                    R_DIE,
                    "Job already seen");
                1;
            } or $log->warn("Failed to mark job already seen - $@");
            $job->{joberr} = 'Already seen this job';
            $job->{jobnative} = c_JOB_ALREADY_SEEN;
            $log->warn(sub {'JOB ALREADY POSTED ' . Dumper($job)});
        } else {
            $log->logwarn("Failed to insert into job_audit, $ev");
        }
        1;
    };
    return if $caught;
    my @now = gmtime(time());
    $job->{jobqed} = sprintf "%d/%d/%d %02d:%02d:%02d",
      $now[3], $now[4]+1, $now[5]+1900, $now[2], $now[1], $now[0];

    push @{$q->{jobs}}, $job;
    $q->{queued}->{$key} = $job->{jobid} if ($key);
    $log->debug("Queued job " . $job->{jobid});
    $total_jobs_on_all_queues++;
    return $job->{jobid};
}
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$clientref if the scalar which 5.10.1 complains about.

my $clientref = $job->{clientref} if (exists($job->{clientref}));
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my with a statement modifier on the end is generally (almost universally?) a bad thing (unless it's a workaround for a weird issue as in ikegami's post). You probably want something like:

my $clientref = exists($job->{clientref}) ? $job->{clientref} : undef;
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Update: Actually, I don't see any reason to not just do (since the value will be undef if the key doesn't exist, and it won't be autovivified in the hash):

my $clientref = $job->{clientref};
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Update: ikegami is correct below. His post did not use "my...if...". My bad :-(

I don't understand why I have to do this.

It's a workaround for a different problem. (You don't use eval EXPR.) I had to guess, since you didn't give me anything but the message to work on.