CS 497C – Introduction to UNIX Lecture 14: - File Attributes

1. CS 497C – Introduction to UNIXLecture 14: - File Attributes Chin-Chih Changchang@cs.twsu.edu

2. 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.

3. 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.

4. 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.

5. 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

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.