Re: mode Q on File::stat

[Abid Khwaja]

Thanks for the pointers.  Here's what I did:

1. stat the file to see the mode set by the system

demerzel:~/etc abid$ ls -l
total 16
-rw-rw----   1 root  uucp  311 Nov 14 15:20 slist.conf
demerzel:~/etc abid$ stat -s slist.conf


2. check for root:uucp and 660

use Fcntl;
use File::stat;

my $etcgroup = "/etc/group";
my $conffile = "/Users/abid/etc/slist.conf";
my $shouldbegroup = "uucp";
my $shouldbeuid = 0;
my $shouldbemode = 0100660;     # -rw-rw---- perms

my $shouldbegid;

sysopen(GROUP, $etcgroup, O_RDONLY)
        || die "can't find/open $etcgroup: $!\n";

while (<GROUP>) {
        if (/^$shouldbegroup/ && /\d+/) {
                $shouldbegid = $&;
                last;
        }
}

close(GROUP)
        || die "can't close $etcgroup: $!\n";

# get config file permissions
my $perms = stat($conffile)
        || die "can't find $conffile: $!\n";

# are permissions set correctly?
unless (($perms->uid == $shouldbeuid) &&
        ($perms->gid == $shouldbegid) &&
        (($perms->mode & $shouldbemode) == $shouldbemode)) {
                print "Aborting!  Incorrect config file perms!\n";
                exit 1
        }


On Nov 24, 2005, at 9:37 PM, John W. Krahn wrote:

st_dev=234881026 st_ino=6858828 st_mode=0100660 st_nlink=1 st_uid=0 st_gid=66 st_rdev=0 st_size=311 st_atime=1132939903 st_mtime=1131999637 st_ctime=1132948249 st_blksize=4096 st_blocks=8 st_flags=0

Abid Khwaja wrote:

I've been trying to figure out how to use File::stat to check file
modes but haven't had much luck understanding how it works from the
documentation.  My goal is to check if a file is owned by a specific
user, group owned by a specific group and has mode 660.  I have the
uid and gid checks down but need help with with the mode check.

The documentation for the stat function explains how to do that:

perldoc -f stat
[snip]
        You can import symbolic mode constants ("S_IF*") and functions
        ("S_IS*") from the Fcntl module:

            use Fcntl ’:mode’;

            $mode = (stat($filename))[2];

            $user_rwx      = ($mode & S_IRWXU) >> 6;
            $group_read    = ($mode & S_IRGRP) >> 3;
            $other_execute =  $mode & S_IXOTH;

            printf "Permissions are %04o\n", S_IMODE($mode), "\n";

            $is_setuid     =  $mode & S_ISUID;
            $is_setgid     =  S_ISDIR($mode);


Also the STAT(2) man page may help.

So I'm doing the following test:

use File::stat;
my $conffile = "/etc/slist.conf";
my $perms = stat($conffile)
   || die "can't find $conffile: $!\n";
my $mode = $perms->mode;
print "$mode\n";

against the following file:

----------   1 joe  uucp  311 Nov 14 15:20 slist.conf

When I run the code, here's what I get:

32768


X box but the code needs to run cross-unix-platform.

The output varies as I change the file mode but I don't see the relation between the code output and the mode. If someone can explain to me how this works, it would be greatly appreciated. I'm running this on a MacOS

permissions.  Of those three bits the least significant bit is execute

permission.  For example:

$ touch TEST
$ chmod 0752 TEST
         ^^^
         ogw

$ ls -l TEST
-rwxr-x-w-  1 john users 0 2005-11-24 18:20 TEST
 ^^^^^^^^^
 ooogggwww

$ perl -le'
use File::stat;
my $st = stat "TEST" or die "stat: $!";
printf "%o\n",  $st->[2];
'
100752
   ^^^
   ogw



John
--
use Perl;
program
fulfillment

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That is because most discussions about the mode assume an octal representation where the three least significant bits are the world permissions and the next three bits are the group permissions and the next three bits are the owner permission and the next bit is write permission and the next bit is read

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