I congratulate you for posting some actual Perl code!
I do have some quibbles with it. For example, you are experienced enough to know never to use $a or $b as a user variable name since these variable names have special meaning within Perl.
I don't want to be overly critical lest I discourage you from posting code.

Update: Three examples should suffice. Ha!

You did not consider blank fields at the beginning of the line.
I don't think that any beginning Perl'er needs to know this, but:

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my $str ="  abc xyz   \n";

my @tokens = split(/\s+/,$str);
print Dumper \@tokens;

=PRINTS:
$VAR1 = [
          '',
          'abc',
          'xyz'
        ];
=cut        

@tokens = split (' ',$str);
print Dumper \@tokens;

# note: leading blank field is not there!
# no need to remove spaces at beginning or end of
# line with this special situation.

=PRINTS:
$VAR1 = [
          'abc',
          'xyz'
        ];
=cut
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