my $tmpdir;
for (qw(TMPDIR TMP TEMP)) {
  next unless $tmpdir = $ENV{$_};
  last if -d $tmpdir;
  die "Invalid temporary directory $tmpdir from \$ENV{$_}\n";
}
$tmpdir ||= "/tmp"; # if this is busted, you got troubles...
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-- Randal L. Schwartz, Perl hacker