$? is the variable that holds the exit status from external commands in Perl. If you just want to know whether the command succeeded, you could do something like this:

system('whatever');
if ($?) {
  warn "whatever failed\n";
}
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If you want to know why the command exited with an error, you could examine the value of $? like this:

system('whatever');
if ($?) {
  my $exit_value  = $? >> 8;
  my $signal_num  = $? & 127;
  my $dumped_core = $? & 128;

  print "whatever exited with status $exit_value";
  print " from signal $signal_num"                    if $signal_num;
  print " and dumped core"                            if $dumped_core;
  print "\n";
}
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(See perlvar and system for more about $?)