#!/usr/bin/perl -w
    use strict;
    open(OUT1, ">file1.txt") || die $!;
    open(OUT2, ">file2.txt") || die $!;
    while(<>){
        print OUT1 if (1 .. /^DETSO1/) =~ /^\d+$/;
        print OUT2 if /^DETSO1/ .. eof;
    }
    __END__