my $n = 0;
while (1) {
  $ENV{"X$n"} = "X" x 1024;
  test($n) or last;
  $n++;
}
print "first failure at n = $n\n";

sub test {
  my $n = shift;
  my $st = system('/bin/echo \\\$X1 >/dev/null');
  # Note: the above call to system() will cause the shell to
  # report 'Argument list too long' for a large enough environment.
  $st == 0;
}