use strict;

my $string
    = 'one two three four five six seven eight nine ten eleven twelve thirteen fourteen fifteen sixteen seventeen eighteen nineteen twenty';

{
    local $, = ', ';
    print first_x( $string, 10 ), "\n";
}

print scalar first_x( $string, 10 ), "\n";

sub first_x {
    return
        wantarray
        ? ( split /\s+/, $_[0], $_[1] + 1 )[ 0 .. $_[1] - 1 ]
        : join ' ', ( split /\s+/, $_[0], $_[1] + 1 )[ 0 .. $_[1] - 1 ];
}