Re: Chmod a+x a file in Perl

[atcroft]

*Nix permissions are based around 3 categories (user, group, and other) and 3 values (read, write, and execute). A value such as 0777 the octal (base-8) value that represents giving each category each of the permissions. The value '7' isn't being "lucky" here-it is the sum of the three bits used to represent the values. The actual meaning of each bit in the value is:

\	Read	Write	Execute	Translation ('rwx')
0	0	0	0	---
1	0	0	1	--x
2	0	1	0	-w-
3	0	1	1	-wx
4	1	0	0	r--
5	1	0	1	r-x
6	1	1	0	rw-
7	1	1	1	rwx

Now take those values and apply by user to your example of 0777:

\	User	Group	Other
Read	4	4	4
Write	2	2	2
Execute	1	1	1
Total	7	7	7

Needless to say, giving anyone and everyone read, write, and execute permissions to a file is a BAD IDEA. (If there was ever a place where the old HTML blink tag might be approrpriate, it was the end of the previous sentence.)

To do the equivalent of 'a+x' you would need to get the current permissions (via stat) and OR ('|') that value with 0111. For each category of user, this gives you the following permissions:

A (rwx)	B	A|B (rwx)
0 (---)	1	1 (--x)
1 (--x)	1	1 (--x)
2 (-w-)	1	3 (-wx)
3 (-wx)	1	3 (-wx)
4 (r--)	1	5 (r-x)
5 (r-x)	1	5 (r-x)
6 (rw-)	1	7 (rwx)
7 (rwx)	1	7 (rwx)

Hope that helps.

[atcroft]

If you want to see all 4096 possible file permissions, the following code will generate each of them in the directory of your choice (named '0nnnn_xxxxxxxxx.txt', where '0nnnn' is the octal permission, and 'xxxxxxxxx' is the string form of the permissions). (Each file contains only the text of its file name, including the provided path.)

Code:

Read more... (6 kB)

Example of created files:

$ ./working --create_dir --target_dir my_foo
$ cd my_foo && ls -labhrt | tail -n 1000 | head -n 10
---S-ws--x  1 User Group 27 Feb 17 23:29 06031_--S-ws--x.txt
---S-ws-w-  1 User Group 27 Feb 17 23:29 06032_--S-ws-w-.txt
---S-ws-wx  1 User Group 27 Feb 17 23:29 06033_--S-ws-wx.txt
---S-wsr--  1 User Group 27 Feb 17 23:29 06034_--S-wsr--.txt
---S-wsr-x  1 User Group 27 Feb 17 23:29 06035_--S-wsr-x.txt
---S-wsrw-  1 User Group 27 Feb 17 23:29 06036_--S-wsrw-.txt
---S-wsrwx  1 User Group 27 Feb 17 23:29 06037_--S-wsrwx.txt
---Sr-S---  1 User Group 27 Feb 17 23:29 06040_--Sr-S---.txt
---Sr-S--x  1 User Group 27 Feb 17 23:29 06041_--Sr-S--x.txt
---Sr-S-w-  1 User Group 27 Feb 17 23:29 06042_--Sr-S-w-.txt

Example of --debug output (d3106 = 06042):

$ ./working --create_dir --target_dir my_foo --debug
# ---skip---

%perm = (
          "octal" => {
                       "0_special" => 3072,
                       "1_user" => 0,
                       "2_group" => 32,
                       "3_other" => 2
                     },
          "octal_value" => {
                             "0_special" => 6,
                             "1_user" => 0,
                             "2_group" => 4,
                             "3_other" => 2
                           },
          "raw_octal" => 3106,
          "str" => {
                     "1_user" => "--S",
                     "2_group" => "r-S",
                     "3_other" => "-w-"
                   }
        );

# ---skip---