in reply to Re^2: Generate a unique ID
in thread Generate a unique ID

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

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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 | ...)

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Re^4: Generate a unique ID
by BrowserUk (Patriarch) on Nov 16, 2010 at 08:16 UTC
    use -X

    -X uses stat and that takes quite a long time, especially on Win32. It leaves the possibility that between your failed attempt and the return of the test, another program (or another copy of this program), will get in and create the directory.

    But as javafan pointed out, that isn't necessary. $! tells me the reason for failure. See Re^4: Generate a unique ID.

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