I am using a Perl script to construct a spark-submit command that will trigger a long running spark job on a Hadoop cluster, then using system() to execute the command. Sometimes, system() returns undef instead of a proper return code, resulting in inaccurate logic flow since undef == 0 evaluates to true.

My current code:

#!/usr/local/bin/perl5.12 -w
#...

my $exitCode = system("$sparkSubmitCmd");
sleep(10);
if ($exitCode == 0) {
    $log->info("$jobName run succeeded.n");
    #Logic if run succeeded
} else {
    $log->error("$jobName run failed.n");
    #Logic if run failed
}

Produced this log with a failed underlying run:

Argument "" isn't numeric in numeric eq (==) at /usr/local/bfm/etc/SCRIPT_NAME.pl line #.
JOB_NAME run succeeded

Where the line # pointed to the $exitCode == 0 if statement.

I know I can switch how undef is treated by adding defined($exitCode) in the if statement, but I don’t want to report false negatives or false positives. This issue has been very difficult to reproduce as it only happens occasionally. I have not been able to determine if a successful execution will ever return undef or not.

Sidestepping the question of whether it’s better to report false negatives or false positives, how do I avoid undef entirely? If that’s not possible, how do I construct the script to determine the run state even in the case of an undef?