CHAN, KENNETH 1 [AG/7721] wrote:
Hi all,
Hello,
I have 2 simple questions (maybe be very trial):
1. I saw some code put "umask 022;" in the near beginning of perl
script. I understand that umask is for changing the file permission in
unix/linux.
No, that is incorrect. umask() by itself does not change a file.
man 2 umask
NAME
umask - set file mode creation mask
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
mode_t umask(mode_t mask);
DESCRIPTION
umask() sets the calling process’s file mode creation mask
(umask) to mask & 0777 (i.e., only the file permission bits of
mask are used), and returns the previous value of the mask.
The umask is used by open(2), mkdir(2), and other system calls
that create files to modify the permissions placed on newly
created files or directories. Specifically, permissions in the
umask are turned off from the mode argument to open(2) and
mkdir(2).
The constants that should be used to specify mask are described
under stat(2).
The typical default value for the process umask is S_IWGRP |
S_IWOTH (octal 022). In the usual case where the mode argument
to open(2) is specified as:
S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH
(octal 0666) when creating a new file, the permissions on the
resulting file will be:
S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH
(because 0666 & ~022 = 0644; i.e., rw-r--r--).
John
--
The programmer is fighting against the two most
destructive forces in the universe: entropy and
human stupidity. -- Damian Conway
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