[Israel.pm] File permissions and File::Copy

Oron Peled oron at actcom.co.il
Mon May 31 14:30:13 PDT 2004


On Monday 31 May 2004 17:15, Offer Kaye wrote:
> What can I do to make File::Copy preserve the file permissions when copying?
> Is this a bug or a feature? :-)

A feature of course... in Unix/Linux every process has a umask field
that is inherited by its child processes. Whenever a file is created by
a process, its initial permission is calculated by *binary substraction*
of the umask value from the permissions asked by the application.

This let the user set a simple "policy" to restrict the default permissions
of files/directories created. You use the shell 'umask' command to view or
set the current umask value and the shell passes this value to all 
subprocesses it creates later.

Example:
  - A process has a umask of 027
  - An application creates (via open) a file with mode 666 (-rw-rw-rw-).
  - The resulting file is 640 (-rw-r-----).
  - Now an application creates a directory with mode 777 (-rwxrwxrwx).
  - The resulting directory is 750 (-rwxr-x---).

As you already answered yourself, you may "copy" the persmissions
from the old file to the new file (stat + chmod). This is exactly what
the '-p' option of the Unix/Linux 'cp' command does.
 
> And no, I don't want to use the shell's copy...

Your latest code fragment is equivalent... good. It was nice
if File::Copy had an *option* to this effect.

-- 
Oron Peled                             Voice/Fax: +972-4-8228492
oron at actcom.co.il                  http://www.actcom.co.il/~oron

"UNIX was not designed to stop you from doing stupid things, because
that would also stop you from doing clever things."
                                                         --Doug Gwyn




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