$data =~ /^(?:(\d+)\s*(?{ push @results, $^N }))+$/;

##</code><code>##

my @results;
while (<DATA>) {
    @results = ();
    /^(?:(\d+)\s*(?{ push @results, $^N }))+$/;
    print "line $.: ", join('-', @results), "\n";
}

__DATA__
1 2 3 4 5
2 3 4 5 6
3 4 5 6 7

##</code><code>##

line 1: 1-2-3-4-5
line 2: 2-3-4-5-6
line 3: 3-4-5-6-7

##</code><code>##

while (<DATA>) {
    my @results;
    /^(?:(\d+)\s*(?{ push @results, $^N }))+$/;
    print "line $.: ", join('-', @results), "\n";
}

##</code><code>##

line 1: 1-2-3-4-5
line 2: 
line 3: