Thanks all - some nice variations... but I'll probably stick with the original (IIABDFI) - that said, here's a 'nicer' version I came up with (which uses a two-element array, plus a push and a shift), but I suspect that the niceness comes at the expense of readability...

use strict;

open(DAT, "export.dat")||die "Cannot open export.dat for read:$!\n";

my @temp_lines;
push @temp_lines, scalar <DAT>;
my $closed = 1;

while($temp_lines[0] !~ /^<EOF>$/){
  open(TEMP, ">temp.dat") if $closed;
  $closed = 0;
  push @temp_lines, (eof DAT) ? '<EOF>' : (scalar <DAT>) ;

  print TEMP shift @temp_lines;

  if($temp_lines[0] =~ /^(1|<EOF>)/){
    close TEMP;
    &output_data();
    $closed = 1;
  }
}
close DAT;

sub output_data{
  print "in output_data\n";
  open(TEST, 'temp.dat')||die "cannot open temp in sub:$!\n";
  while(<TEST>){
    chomp;
    print "$_\n" if $_ =~ /\S/;
  }
  print "end of output_data\n";
}
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map{$a=1-$_/10;map{$d=$a;$e=$b=$_/20-2;map{($d,$e)=(2*$d*$e+$a,$e**2
-$d**2+$b);$c=$d**2+$e**2>4?$d=8:_}1..50;print$c}0..59;print$/}0..20
[download]