\w+ doesn't match spaces. Use [^\]]+ instead:
$errmsg =~ /^((?:\[[^\]]+\]){3})(.*)/; or
$errmsg =~ s/^(?:\[[^\]]+\]){3}//;

Update: The directions were correct, but the code was missing a set of parens.

In reply to Re: Problem parsing an error msg with regex by ikegami
in thread Problem parsing an error msg with regex by periapt

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