The subdirectory message is being sent to STDERR by the 'md' command not Perl.

I found this in the Perl documentation with regards to what $res is being assigned,

The collected standard output of the command is returned; standard error is unaffected. In scalar context, it comes back as a single (potentially multi-line) string, or undef if the command failed.

In reply to Re: WHY error message is printed in STDOUT? by Herkum
in thread WHy error message is printed in STDOUT? by madtoperl

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