#!/usr/bin/perl -w
use strict;

my $curr_chrom = "";

while (<DATA>)
{
   my ($chrom) = split;  # $chrom is the first column
                         # parens on the left side are needed
                         # for list context
   if ($chrom ne $curr_chrom)
   {
       $curr_chrom = $chrom;
       open (OUT, '>', "$curr_chrom.out") 
          or die "unable to write $curr_chrom.out $!\n";
   }
   print OUT;
}
close OUT;


__DATA__
chr1    100 159 0
chr1    200 260 0
chr1    500 750 0
chr3    450 700 0
chr4    100 300 0
chr7    350 600 0
chr9    100 125 0
chr11   679 687 0
chr22   100 200 0
chr22   300 400 0

##</code><code>##

while (<KEY>) {

    chomp;
    @key_split = split("\n");
    $Chr{"$key_split[0]"} = $key_split[0];
}
## better written as: ##
while (<KEY>) {
    my ($chrom) = split;
    $Chr{$chrom}=1;
}