It finds a non-digit and replaces it with a space. If you want it to do it repeatedly, use /g. 
$nums =~ s/\D/ /g;

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See s/PATTERN/REPLACEMENT/... under "Regexp Quote-Like Operators" in perlop. ( er, the documentation of /g was moved to perlre in 5.10 )

In reply to Re: Getting Trouble with REGEXP by ikegami
in thread Getting Trouble with REGEXP by Oromis92

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