abs

#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';
sub error {
  my ($x1, $y1, $d1, $x2, $y2, $d2) = @_;
  return undef if abs($x1 - $x2) > .20001 || abs($y1 - $y2) > .20001;
  return [$d1, $d2];
}
my $data1 = []; my $data2 = [];
open my $d1, '<data1.dat' or die; open my $d2, '<data2.dat' or die;
while (<$d1>) {
  next if /\Ax座標/;
  chomp; my @d = split; push @$data1, \@d;
}
while (<$d2>) {
  next if /\Ax座標/;
  chomp; my @d = split; push @$data2, \@d;
}
close $d1; close $d2;
my $size1 = scalar @$data1; my $size2 = scalar @$data2;
open my $out, '>output.dat' or die;
for (my $i = 0; $i < $size1; $i++) {
  for (my $j = 0; $j < $size2; $j++) {
    my @d = (
      $data1->[$i][0], $data1->[$i][1], $data1->[$i][2],
      $data2->[$j][0], $data2->[$j][1], $data2->[$j][2]
    );
    my $error = error @d;
    next unless defined $error;
    say $out join "\t", @$error;
  }
}
close $out;