File

Listing File

ls- listing files in current directory

ls -l will help you get more information of the files

To list the invisible files, specify the -a option to ls −

Copying Files

To make a copy of a file use the cp command. The basic syntax of the command is −

1	$ cp source_file destination_file

Renaming Files

To change the name of a file, use the mv command. Following is the basic syntax −

1	$ mv old_file new_file

The mv command will move the existing file completely into the new file. In this case, you will find only newfile in your current directory.

File Permission

Every file in Unix has the following attributes −

Owner permissions − The owner’s permissions determine what actions the owner of the file can perform on the file.
Group permissions − The group’s permissions determine what actions a user, who is a member of the group that a file belongs to, can perform on the file.
Other (world) permissions − The permissions for others indicate what action all other users can perform on the file.

The permissions are broken into groups of threes, and each position in the group denotes a specific permission, in this order: read (r), write (w), execute (x) −

The first three characters (2-4) represent the permissions for the file’s owner. For example, -rwxr-xr– represents that the owner has read (r), write (w) and execute (x) permission.
The second group of three characters (5-7) consists of the permissions for the group to which the file belongs. For example, -rwxr-xr– represents that the group has read (r) and execute (x) permission, but no write permission.
The last group of three characters (8-10) represents the permissions for everyone else. For example, -rwxr-xr– represents that there is read (r) only permission.

When we use ls -l command, the permission information will be shown.

The first character represent what type it is.

- represents a file

d represents a directory

Change Permission

We have two modes to change the permission of files.

Symbolic Mode

a ->all（user，group，other）
u ->user
g ->group
o ->other

	Chmod operator & Description
+	Adds the designated permission(s) to a file or directory.
-	Removes the designated permission(s) from a file or directory.
=	Sets the designated permission(s).

Example

$chmod o+wx testfile
$ls -l testfile
-rwxrwxrwx  1 amrood   users 1024  Nov 2 00:10  testfile
$chmod u-x testfile
$ls -l testfile
-rw-rwxrwx  1 amrood   users 1024  Nov 2 00:10  testfile
$chmod g = rx testfile
$ls -l testfile
-rw-r-xrwx  1 amrood   users 1024  Nov 2 00:10  testfile

Absolute Permissions

The second way to modify permissions with the chmod command is to use a number to specify each set of permissions for the file.

Each permission is assigned a value, as the following table shows, and the total of each set of permissions provides a number for that set.

Number	Octal Permission Representation	Ref
0	No permission	—
1	Execute permission	–x
2	Write permission	-w-
3	Execute and write permission: 1 (execute) + 2 (write) = 3	-wx
4	Read permission	r–
5	Read and execute permission: 4 (read) + 1 (execute) = 5	r-x
6	Read and write permission: 4 (read) + 2 (write) = 6	rw-
7	All permissions: 4 (read) + 2 (write) + 1 (execute) = 7	rwx

Here’s an example using the testfile. Running ls -1 on the testfile shows that the file’s permissions are as follows −

1 2	$ls -l testfile -rwxrwxr-- 1 amrood users 1024 Nov 2 00:10 testfile

Then each example chmod command from the preceding table is run on the testfile, followed by ls –l, so you can see the permission changes −

$ chmod 755 testfile
$ls -l testfile
-rwxr-xr-x  1 amrood   users 1024  Nov 2 00:10  testfile
$chmod 743 testfile
$ls -l testfile
-rwxr---wx  1 amrood   users 1024  Nov 2 00:10  testfile
$chmod 043 testfile
$ls -l testfile
----r---wx  1 amrood   users 1024  Nov 2 00:10  testfile

basic operations