Using open

Open will follow symlinks and dangling symlinks.

It's tempting to do stat calls first to be sure you're not tricked, but that's still a race condition.

If you're sure the file should not exist before you create it, use the O_EXCL flag to open.

    fd = open( FILENAME, O_CREAT | O_RDWR | O_EXCL, 0666 );

or for Perl folks

    use Fcntl;
    sysopen( HANDLE, $filename, O_CREAT | O_RDWR | O_EXCL ) or die;
       # mode defaults to 0666
       # perldoc perlopentut for more wonders