Here's a snippet of code that implements what you describe: 
sub fuzzy {
    my $string = shift;
    my @alt;
    for(my $i = 0; $i < length($string); $i++) {
        my $alt = $string;
        substr($alt, $i, 1) = 'N';
        push @alt, $alt;
    }
    return join '|', $string, @alt;   # original too
}

print fuzzy('GCGAT');

[download]
You can just do 
$re = fuzzy($string);
if($value =~ /^($re)/) { ... }

[download]
Note the parens for grouping.

If there's only one value for $re during the run of the file, you can use /o (as in /^($re)/o) but in a modern perl I don't think that makes much difference.

In reply to Re^2: string match using with an N in any position by bart
in thread string match using with an N in any position by biobee07

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