in reply to How to extract all alphanumeric characters from a string?

utf8::upgrade( my $alphanums = $chars );
$alphanums =~ s/[\W_]//g;

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or 
( my $alphanums = $chars ) =~ s/\P{Alnum}//g;

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utf8::upgrade makes /\w/ match alphanums and "_", and /\W/ everything else.

Update: The original solution didn't remove underscores. Fixed.
Update: Added alternative method.

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