Now that you have a basic understanding of the filesystem and how to navigate it, you can begin creating and managing your own files and directories. Let's begin with directories. You create directories with mkdir and remove them with rmdir.

Exercise 4.1

Create two new directories with the mkdir command (use the ls command to confirm the new directories were created).

          % mkdir test test2 

Now remove the second directory you just created (and list the files in the current directory again to see if the second directory was removed).

          % rmdir test2 

Let's move on to working with files. First, you'll need to copy some existing files from elsewhere in the filesystem into your test directory. You use the cp command to do this.

Exercise 4.2

Before going on, move into the new "test" directory you just created. You will use this area to experiment (thus minimizing any potential damage to other files in your home directory!).

          % cd test
          % pwd
          /home/natasha/test 

Now you can copy some files into your test directory with cp.

          % cp /etc/motd .
          % cp /etc/hosts .
          % cp /etc/group .
          % ls
          group   hosts   motd 

The three cp commands above copy existing files from the "/etc" directory into the current directory (repesented by ".").

Now remove (delete) a file using the rm command.

% rm group
          % ls
          hosts   motd 

Finally, move (rename) one of the files using mv.

          % mv motd message-of-the-day
          % ls
          hosts   message-of-the-day 

Both cp and mv require two arguments: the existing location and the destination of the file to be copied or moved. The destination can be another file or a directory. Let's compare the results in each case.

Exercise 4.3

First, let's make a new directory within the test directory.

          % mkdir junk
          % ls
          hosts     junk/     message-of-the-day 

Then try the following command:

          % cp hosts hosts2
          % ls
          hosts           junk/
          hosts2          message-of-the-day 

The result in this case is a second copy of the file (called "hosts2") in the current directory. Now try the following:

          % cp hosts junk
          % ls
          hosts           junk/
          hosts2          message-of-the-day
          % ls junk
          hosts 

This time, the file was copied to the "junk" directory, keeping the same name as the original ("hosts").

Exercise 4.4

Make yet another directory.

          % mkdir stuff
          % ls
          hosts                junk/                stuff/
          hosts2               message-of-the-day 

Now repeat the cp command from the last exercise using a wildcard.

          % cp hosts* stuff
          % ls stuff
          hosts     hosts2 

Both "hosts" and "hosts2" were copied this time.

Exercise 4.5

Copy the "junk" directory and its contents to a new location.

          % cp -r junk more-junk
          % ls
          hosts                junk/                more-junk/
          hosts2               message-of-the-day   stuff/
          % ls more-junk
          hosts 

The result in this case is a new directory ("more-junk") whose contents are the same as the "junk" directory. Next, remove the "more-junk" directory and its contents.

          % rm -r more-junk
          % ls
          hosts                junk/               stuff/
          hosts2               message-of-the-day 

UNIX provides permissions (also known as modes) to restrict access to your files and directories. These are manipulated with the chmod ("change modes") command. Recall that ls -l shows a long listing of files and directories. The first column in this long listing is a 10-character string indicating the type of file (regular file, directory, link, etc.) and the access permissions for the file's owner, group, and other users. This is broken down in Table 4.1.

Table 4.1

File Type (character 1)	Owner Access (characters 2-4)	Group Access (characters 5-7)	Other Access (character 8-10)
- = regular file d = directory	r = read w = write x = execute	r = read w = write x = execute	r = read w = write x = execute

        drwxr-x--- 

The chmod command uses a special argument (composed of three parts as summarized in Table 4.2) to assign the desired rights to files or directories.

Table 4.2

Entity	Operator	Access Right
u = user (owner) g = group o = others a = all of the above	+ = grant - = revoke = = set	r = read w = write x = execute - = no access

        u=rw-,g=r--,o=--- 

Add all rights for owner and revoke all rights for group and others on the "hosts" file.

          % ls -l hosts
          -rw-r--r--  1 natasha  staff   983 Apr 12 01:08 hosts
          % chmod u+rwx,g-rxw,o-rwx hosts
          % ls -l
          -rwx------  1 natasha  staff   983 Apr 12 01:08 hosts
          

Now add read access for the group.

          % chmod g+r hosts
          % ls -l
          -rwxr-----  1 natasha  staff   983 Apr 12 01:08 hosts