use warnings;
use strict;
use File::Glob ':bsd_glob';

my @infiles = sort glob 'SBNUM_*.txt';
my $outfile = 'v2test.txt';

open my $ofh, '>', $outfile or die "$outfile: $!";
my ($prevleft,$prevright);
for my $infile (@infiles) {
	open my $ifh, '<', $infile or die "$infile: $!";
	while (<$ifh>) {
		my ($left,$right) = /^(\d{3}),-->(\d{3}),$/
			or die "Couldn't match '$_'";
		if (defined $prevleft) {
			print $ofh "$prevleft,-->$right,\n";
		}
		($prevleft,$prevright) = ($left,$right);
	}
	close $ifh;
}
close $ofh;