Lab46 Wiki

To be able to effectively use a UNIX system, one must become familiar with the basic tools, as well as be able to know how to use the online manual.

This lab provides an introduction to many fundamental concepts.

In “UNIX for the Beginning Mage”, please read:

• Chapter 3 (pages 20-36).

In “Harley Hahn's Guide to UNIX and Linux”, please read:

• Chapter 9 (“Documentation: The UNIX Manual and Info”, pages 189-221).
• Chapter 10 (“Command Syntax”, pages 223-237).
• Chapter 24 (“Working with Directories”, pages 659-714).
• Chapter 25 (“Working with Files”, pages 715-766).

In “Learning the UNIX Operating System, 5th Edition”, please read:

• Selections from Chapter 3 (“Using Your UNIX Account”):
  • “The UNIX Filesystem”, pages 42-54.
  • “Looking Inside Files with less”, pages 54-55.
  • “Completing File and Directory Names”, page 62.

• Selections from Chapter 4 (“File Management”):
  • “File and Directory Names”, pages 66-67.
  • “File and Directory Wildcards”, pages 67-69.
  • “Managing Your Files”, pages 74-80.

It has been said that the UNIX environment is terse and unfriendly. Terse at times it may be, but once the commands are understood and appreciated, the environment becomes a strong ally.

Only the original creators of UNIX could ever really explain their reasoning for naming certain commands the way they did. ls for list, cp for copy, and of course rm for remove are among the many such examples.

If you look at something from a space-efficient perspective, perhaps this naming scheme starts to make more sense.

Can you make out the meaning of a word if you remove all the vowels? Perhaps. How about a pattern of letters?

Let's take a list of basic commands and apply a simple rule:

Keep the first and third letter of the word the command represents, and drop the rest.

Ok, let's try a few commands:

While the rules don't work for very many additional commands besides these basic utilities, perhaps it'll help you remember these basic few.

Hopefully, you will see all the files in the base of your home directory. For most of you, they should also appear colored. And no, it's not just to make it look pretty.

For starters, see those (hopefully) medium blue files called bin, public_html, and src? Those are actually directories. The color scheming system will make all directories that color.

That is how the coloring scheme works- it color codes by file type.

But isn't a directory different from a file? That's one of the wonderful things about UNIX that we'll encounter later- Practically everything on the UNIX filesystem is a file. A directory, then, is a file that contains the locations of other files.

Let's play a little with ls. It will undoubtedly be a useful command.

What we've just done is invoke ls with an argument, namely the -l. Traditionally, UNIX accepts arguments with the dash followed by a letter, in the form of a short argument. Long arguments also exist, and are commonly invoked by two dashes followed by a longer argument name. Remember, tradition is important in UNIX. You'd do well to take note of these things, as you never know where you'll encounter them later.

So, back to what you see on the screen. Let's take a close look at the line for your src directory:

lab46:~$ ls -l
drwxr-x--- 2 js001234 users 4096 Sep 24 16:58 src

While most of this information will be covered later, it will be important to understand generally what is seen here. In brief, the “drwxr-x—” on the left represent the permissions for that particular file. Looking at other files will yield different permissions.

Next, skip over to the 3rd column… instead of the “js001234” listed here, your own username should be present. This column represents the user on the system that owns that particular file, in this case- you.

Following that is the group owner of the file. This may be set to “users” or “unix”, depending on what other courses you are enrolled in. More on groups later.

Then you will come to the numeric value. This represents the size of the file in bytes. So the 4096 here would mean the file is 4kB in size.

The timestamp of the file follows, which basically is the time of modification/creation.

Lastly, is the name of the file itself.

To copy a file or files, the cp command is used. For people familiar with DOS, you will notice it works in the same fashion. The basic format of the command is: cp source destination

lab46:~$ cp /etc/motd .
lab46:~$ 

lab46:~$ cp motd lab1.text
lab46:~$ 

In UNIX, there is no rename command, however the same functionality can be accomplished by moving a file to a new name.

The mv command has the same format as the cp command just discussed. Let's use it to rename the motd file:

lab46:~$ mv motd lab1a.txt
lab46:~$ 

Get a file listing, you should notice the change.

Now to actually move a file into another directory:

lab46:~$ mv lab1.text src
lab46:~$ 

A file listing will show that lab1.text is no longer present in the base of your home directory. If you look in your src/ subdirectory, you should find the file.

The rm command allows you to remove files.

Let's remove that file in your src/ directory:

lab46:~/src$ rm lab1.text
rm: remove regular file `lab1.text'? y
lab46:~$ 

You will probably be prompted to ask if you are SURE you want to delete the file. This is to provide a layer of protection between what you say and what the system does. Answer y to go ahead and delete it.

Be sure to change back to the base of your home directory.

There exists a mechanism in UNIX to create a link to a file. This is accomplished via the ln command. The common invocation will be of the form: ln [-s] realfile linkfile

The -s argument to ln tells it to make a soft link. This is usually preferable over the hard link, which actually creates a file in the resulting directory of the same size as the linked file.

Create a symbolic link to your src/ directory:

lab46:~$ ln -s src lab1
lab46:~$ 

Do an ls -l, and take notice to the lines pertaining to src and lab1. lab1 points to src, so operations that can be done on lab1 will also effect src.

lab46:~$ rm lab1
rm: remove symbolic link `lab1'? y
lab46:~$ 

You will notice that lab1 is now gone, but the original src/ remains.

Last, but not least, are the manual pages. These are the online documentation of all the various commands and library functions on a system.

To view a command's manual page, simply type man followed by the command. This will bring up the standard section of the man page for that command, if it exists.

For example:

• cp(1) would mean to reference the section 1 manual page for cp.
• printf(3) would reference the section 3 manual page for printf.

To view a man page in a particular section, you would do the following: man [section] command

lab46:~$ man 3 printf

In the man pages, the particular command is defined, its options given, as well as any other information the developer/packager wanted to include.

To navigate, use the up & down cursor keys to scroll one line at a time. The space bar skips ahead an entire screen.

To exit out of a manual page, hit q

Becoming familiar with and using the manual pages will be important throughout the entire course.

All questions in this assignment require an action or response. Please organize your responses into an easily readable format and submit the final results to your instructor.

Your assignment is expected to be performed and submitted in a clear and organized fashion- messy or unorganized assignments may have points deducted. Be sure to adhere to the submission policy.

The successful results of the following actions will be considered for evaluation:

• your responses to questions submitted at the following form:

<html><center><a href=“http://lab46.corning-cc.edu/haas/content/unix/submit.php?lab1”>http://lab46.corning-cc.edu/haas/content/unix/submit.php?lab1</a></center></html>

• the response from the form (received via e-mail) saved as lab1.txt to your ~/src/unix/ directory
• addition/commit of ~/src/unix/lab1.txt into your repository (CS 0x0 sets you up to do this).

As always, the class mailing list and class IRC channel are available for assistance, but not answers.