Unwanted empty value in array after Splitting a string

[monkfan]

Dear Fellow monks,

I wanted to extract the N segment of a string, and I uses split for that. But why my script below results in the unwanted empty value ('') in the final array (see the Dumper output below).

perl -MData::Dumper -e '
$str = "GTGNNTNNG"; 
@nseg = split(/[ATCG]+/,$str); 
print Dumper \@nseg;'

$VAR1 = [
          '',  # Why this extra???
          'NN',
          'NN'
        ];

[explorer]

split is returning the first empty field, to the left of the first GTG separator in string.

Please, read the first paragraph of split at perldoc.perl.org: http://perldoc.perl.org/functions/split.html

[BrowserUk]

Use grep in conjunction with length to get rid of it.

print for grep length, split '[ACGT]+', "GTGNNTNNG";;
NN
NN

[grep]

Straight from perldoc -f split


Splits the string EXPR into a list of strings and returns that
list.  By default, empty leading fields are preserved, and
empty trailing ones are deleted.

The only exemption is the pattern split(' ',$str) so just add a grep

perl -MData::Dumper -e '
$str = "GTGNNTNNG"; 
@nseg = split(/[ATCG]+/,$str); 
@nseg = grep {/./} @nseg;
print Dumper \@nseg;'

[davido]

As the gang has already pointed out, the documentation for split dispells the mystery. If you're trying to eliminate all empty fields, the grep trick that BrowserUk illustrated is a good solution. But if you're only trying to eliminate one or two (or a few) leading empty fields, you can do this:

shift @nseg until length $nseg[0];

...of course that's not going to help if @nseg contains nothing but empty fields. ;)

[swampyankee]

This is documented behavior: see Split

"Splits the string EXPR into a list of strings and returns that list. By default, empty leading fields are preserved,..."

There's an empty leading field before the first "G".