once >>8 is applied to the value returned by system

First, note you should be checking the whole return value of system, not just the upper byte. If the call was successful, its whole return value should be zero, so you might actually be missing error conditions. Once the return value of system is nonzero, then you can inspect it, as the docs show. You can also consider using IPC::System::Simple, which provides a drop-in replacement for system with nicer error handling.

I've been unable to either reliably reproduce the behaviour (it just happens sometimes in processes running on the server) nor stop it happening. ... I've not been able to find a known bug

IMHO, I would consider it likely then that it's actually the subprocesses that is in fact failing somehow. Adding detailed logging to the process doing the system would probably help in hunting down the problem. For that, consider also capturing the output of the process being run, especially its STDERR, using e.g. Capture::Tiny.

In reply to Re: system >> 8 is non-zero when child exits with exit(0) by haukex
in thread system >> 8 is non-zero when child exits with exit(0) by bjdean

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