EDIT: Testing with a 1000-character randomly generated string for 100000 iterations: $str =~ s/[^a-zA-Z8-9 ]//g; : 30 seconds
$str =~ s/[^a-z8-9 ]//ig; : 29 seconds
$str =~ s/[^a-zA-Z8-9 ]+//g; : 11 seconds

I wouldn't have expected the i flag solution to be more efficient, but there you go. There are significant savings from +. The most efficient regex therefore is: 

$str =~ s/[^a-z8-9 ]+//ig;

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EDIT: You're right, tr/// is much faster.

In reply to Re: regex to remove all non a-z and spaces by TedPride
in thread regex to remove all non a-z and spaces by coldfingertips

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