use -X 
unless (mkdir $dir) {
  -d $dir && ... dir exists;
  -w _ || ... not writable by euid
  -x _ || ... not traversable by euid
}

[download]
if you look for atomic test, you can also open files with O_CREAT | O_EXCL. Then, you can just use pid + start time + local counter 
$fh = IO::File->new ($filename, O_EXCL | O_CREAT | ...)

[download]

In reply to Re^3: Generate a unique ID by happy.barney
in thread Generate a unique ID by BrowserUk

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