If the error returned is >128, subtract 128 to get the signal number. 139-128=11, SIGSEGV, segmentation violation.

The following is from perldoc -f system:

You can check all the failure possibilities by inspecting `$?' like this:

$exit_value  = $? >> 8;
$signal_num  = $? & 127;
$dumped_core = $? & 128;
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-rr