Re: Removing Flanking "N"s in a DNA String

[inman]

A pair of substitutions with a regular expression anchored to the start and end of the string will help.

$dna = "NNNNATCGNNNTCGANNN";
$dna =~ s/^[N]+//;
$dna =~ s/[N]+$//;
print "$dna\n"
__END__
ATCGNNNTCGA

[ikegami]

No need for the square brackets:

$dna = "NNNNATCGNNNTCGANNN";
$dna =~ s/^N+//;
$dna =~ s/N+$//;
print "$dna\n"
__END__
ATCGNNNTCGA

[davidrw]

As metioned already, no need for the character class.. Also, (although i tend to prefer the 2 separate statements as well), this can be written as one:

$dna =~ s/(^N+|N+$)//g;

[blazar]

Also,

s/(?:^N+|N+$)//g;

since we don't really need capturing. Which makes me think that ideally one may want it, instead, to see the text that has been substituted. But then he would only get the N's at ^ (if any) as $1 or . Which in turn make me wonder why there's this asymmetry between s/// and m//, since the latter, in list context and with /g does return all captures while the former just returns a true (or false) value in any context, precisely the numer of matches (or the empty string)...

[blazar]

Why do you need those charachter classes?

s/^N+//, s/N+$// for $dna;