I'm not particularly fond of the extra trip through the sub when we could use a lexical to store the data:

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

then again, I don't like the 0..n slice. Why not just use pop?

sub first_x {
    my @data = split /\s+/, $_[0], $_[1] + 1 ;
    pop(@data); #throw away last element    
    return
        wantarray
        ? @data
        : join ' ' , @data
        ;
}
[download]

peace, spazm