CS 497C – Introduction to UNIX
Lecture 14: - File Attributes
Chin-Chih Chang
chang@cs.twsu.edu

ls: Listing Files
* When you use the ls command, you will see a list of filenames arranged 
  in ASCII collating sequence.
* You can use ls with the filename to know whether a particular file is 
  available.
* Use the –x option to produce a multicolumn output.
* Use the –F option to identify directories and executables.

ls: Listing Files
* The * indicates the file is an executable code.
* The / indicates the file is a directory.
* The –a (all) option lists all hidden files.
* Hidden files are those beginning with a dot.
* Generally, these dot files are startup files for their corresponding 
  commands.
$ ls –Fax
./              ../           .Xauthority      .cshrc*      .cshrc.dec*
.cshrc.linux*   .cshrc.next*  .cshrc.solaris*  .cshrc.sun*  .login*
* . represents the current directory.

ls: Listing Files
* .. represents the parent directory.
* When ls is used with the directory, it shows the contents of the 
  directory.
* The –R (recursive) option lists all files and subdirectories in a 
  directory.
* The –l (long) option of ls reveals most attributes of a file – like 
  its permissions, size, and ownership details.

ls –l: List File Attributes
kirk> ls -l
total 7
drwxr-xr-x      2   cs497c   grader    1024 Sep 25 11:30 bin
-rw-------      1   cs497c   grader     306 Sep 26 11:55 chap3
-rw-------      1   cs497c   grader     306 Sep 26 11:55 chap5
drwx------      2   cs497c   grader    1024 Sep 25 14:35 mail
drwx------      2   cs497c   grader    1024 Sep 25 18:20 nsmail
drwx------      2   cs497c   grader    1024 Sep 26 12:03 prog1

Permissions Links   Owner    Group     size     Last     Filename
                             Owner        Modification Time

ls –l: List File Attributes
* The words total 7 indicates a total of 7 blocks are occupied by these 
  files in the disk.
* The first column shows the type and permissions associated with each 
  file.
* When you create a file, you automatically become its owner.
* When opening a user account, the system administrator also assigns the 
  user to some group.

ls –l: List File Attributes
* The fourth column stands for the group owner of the file.
* The fifth column shows the size of the file in bytes.
* The next set of three columns indicates the last modification time of 
  the file.
* The last column displays the filenames.
* The –d (directory) option force ls to list the directory attributes 
  rather than its contents.

File Permissions
$ ls -l chap3 chap5 hello.sh
-rw-r--r--     1 cs497c   grader        306 Sep 26 11:55 chap3
-rw-------     1 cs497c   grader        306 Sep 26 11:55 chap5
-rwxr-xr-x     1 cs497c   grader         20 Sep 27 23:40 hello.sh

* The first column represents the file permissions. 
* r indicates read permission, which means cat will display the file.
* w indicates write permission, which means you can edit this file.

File Permissions
* x indicates execute permission; the file can be executed as a program.
* There are three categories of users: owner, group, and others.

    owner’s permissions                 other’s permissions
   -     r   w   x         r   -   x         r   -   x
type of file           group’s permissions

* The first group (rwx) indicates the file owner can read, write, and 
  execute this file.

File Permissions
* The second group (r-x) indicates the group can read and execute the 
  file.
* The third group (r-x) indicates others can read and execute the file.