Mac OS X Leopard - ARCAism

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CHAPTER 18 INTRODUCING DARWIN AND THE SHELL
This would effectively just add write permissions to the group for filename.
Suppose you create a file and then wish to give special permissions to a group of people. By
default, any file you create will have both the owner and group listed as you. You can change the
group file to any other group that you belong to using the chgrp command with the following
syntax:
chgrp group filename
To find out what groups you belong to you (and thus what’s available to you), you can use
the id command, like so:
Leopard:~ scott$ id
uid=501(scott) gid=501(scott) groups=501(scott), 81(appserveradm),
79(appserverusr), 80(admin)
So in this case, if I wanted to allow anyone in the admin group to be able to write to my
soliloquy4 file, I could do the following:
Leopard:~/Documents/Shakespeare/macbeth scott$ chgrp admin soliloquy4
Leopard:~/Documents/Shakespeare/macbeth scott$ ls -l
total 8
-rw-r--r--- 1 scott admin 409 May 17 10:44 soliloquy4
Leopard:~/Documents/Shakespeare/macbeth scott$ chmod g+w soliloquy4
Leopard:~/Documents/Shakespeare/macbeth scott$ ls -l
total 8
-rw-rw-r--- 1 scott admin 409 May 17 10:44 soliloquy4
ACLs and Extended File Attributes
ACLs (access control lists) and extended attributes were introduced to OS X in Tiger (OS X 10.4),
but while they used to simply be an option available to those who wished to use them, in
Leopard they are used by default.
NOTE ACLs will only be available on your system locally if you are using the HFS+ file system.
For network shares, they can be used over AFP and SMB/CIFS.
ACLs allow fine-grained control of a file’s access far beyond UNIX’s traditional ownergroup-everyone
permissions. With ACLs you can control specific permissions for specific users
or groups, and you can treat each user and group differently.
Specifically, each file on your system has one ACL, and each ACL may contain an ordered
list of entries. Each entry sets specific permissions for a single user or group.
NOTE If you have a user and a group with the same name, and you must differentiate these in
an ACL, you may prefix the name with either user: or group: to specify which entity you are
referring to.
Files with entries in their ACL will include a + in the 11th character in the permission listing
when you use ls -l. If there are no ACL entries, but there are other file attributes for the given
file, then the 11th character will contain an @. If there are no ACL entries or attributes, then the
11th character will contain a -.
To view the ACL associated with a file, use the -e option with the ls command—for example,
if I look in my home directory: