Creates the directory specified by FILENAME, with permissions specified by MODE (as modified by
umask). If it succeeds it returns TRUE, otherwise it returns FALSE and sets
In general, it is better to create directories with permissive MODEs, and let the user modify that with their
umask, than it is to supply a restrictive MODE and give the user no way to be more permissive. The exceptions to this rule are when the file or directory should be kept private (mail files, for instance). The perlfunc(1) entry on
umask discusses the choice of MODE in more detail.