The problem here is that if $Anytext doesn't match the RE, it'll tell me the RE is invalid

If $RE is not a valid regex, then it will throw an error, which you can catch with a BLOCK eval

my $is_valid = eval { qr{$RE}; 1 }
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should work (not tested).

You could also use some modules like Regexp::Parser or YAPE::Regex if you don't want to interpolate the regex without knowing first if it's valid.