Computer Science 1 - Lab 1
Introduction to Unix
Introduction
============
This guided lab will introduce you to the Unix command line
environment. The objectives of this lab are:
- Work with files in your account including copying files,
renaming files, and removing files.
- Use Manual Pages
- Organize files including using commands to create directories,
changing to a directory, viewing the contents of a directory,
and copying files to a directory.
This lab is a completely guided lab. All you need to do is
carefully read the instructions and execute the commands. You are
encouraged to take notes about the commands that you execute.
In order to use this lab, you will need to be connected to a
Unix-like machine. This can be a local Linux machine, a mac os X
machine, or it can be a shell account on a Unix server. If you do
not own a Unix machine, you can get shell access at sdf.org. You
will need an arpa level membership to do the later labs.
Whatever your setup, I will leave it to you to figure out how to get
into the shell. You will either need to ssh or launch a terminal
application to get the shell going. I have no way of knowing your
setup, but I'm sure with a little googling you'll be good to go.
In this tutorial, I will assume you are logged onto sdf.org. If you
are not, some of the exact paths might be different. More detailed
treatments of Unix are available at
http://sdf.org. This lab will
get you just far enough to be able to write a bit of code.
Now, Let's get started!
Working with files and the Manual
=================================
Ok, so now have a shell open. Great! Exciting stuff! But what
should you do with it? Well, that's where we are heading next. We
will look at how to explore the file system, and how to use the UNIX
manual to get help. This will seem a little overwhelming at first,
but with a little bit of practice, you'll be a CLI pro in no time!
1. Logon / Start the shell.
2. When you logon, you start out in something called your home
directory. Just like in windows, Unix divides its file system up
into directories (folders) and files. Your home folder is your
little slice of the server. In general, this is the only area
you will be able to write data to, and no one else will be able
to read or write to your folder (unless you grant them permission
to do so). So now, let's see where home is. Type the following
command and press enter:
pwd
pwd, which stands for "present working directory", simply displays
the directory you are currently in.
3. Another similar command is "hostname". Go ahead and type it and
press enter. This shows us the name of the server you are
currently connected to.
4. Just like in the rest of the universe, you are not alone on this
server! Type "who" and press enter to see who else is logged in.
5. The screen is getting very cluttered. Type clear and press enter
to clear it.
6. At this stage, let's play around with some generic parts of the
interface. Press the up and down arrows. Note that you can
scroll through the history of the commands you have executed. To
repeat a command on this list, simply press enter. You can also
use the arrow keys and backspace to edit your present command.
Play around with this a little bit now.
7. Ok, now let's move on to some file operations. The first step
is to look at what is in your home directory. Type "ls" and
press enter.
8. If this is a new account, there is not much to look at is it?
Well it stands to reason, you haven't done anything yet, so you
don't have any files yet! Let's try another command. Type "ls
-al" and press enter. Note that there is a space between the
command name and the arguments. This is important! At the top
of the listing, you should see something that looks like this:
drwxr-xr-x 2 c1010a20 students 4096 May 27 20:17 .
drwx--x--x 6 c1010a20 students 4096 May 27 16:19 ..
It looks like you have something after all! You have . which is
your current directory, and .. which is the directory one level
higher than where you presently are. So why did these not appear
when you typed "ls"? The answer is that these special files
begin with a "." which hides them from the ls command. The -a
causes ls to list all the files (including hidden files). This
isn't for security, this is to keep settings and things you don't
want to worry about all the time hidden from view so they don't
get in the way.
The "l" part of the -al means "list details". This shows a lot
of information, including some strange alchemy on the left hand
side. Here's what that stuff means. The first letter, which is
a "d" in this case, indicates that these are directories. This
is followed by 9 characters representing the file's permissions.
In Unix, the permissions are:
r - read
w - write
x - execute
There are three types of people we set this for. There is the
owner of the file, the group of the file, and the rest of the
world. These are the groups represented here. We'll talk more
about permissions in a later lab. The good news is that these
permissions will usually take care of themselves. They are only
important if you want to share things with other users.
9. Speaking of other users, let's take a look at another user's home
directory. Namely, let's look at mine. Type:
ls ~pngwen
This is a reference to my home directory. ~<username> is an
absolute path name for a user's home directory, and is short hand
for my real directory (which is /arpa/ns/p/pngwen)
10. Alright, now we can list folders, let's look at some files. Type
ls ~pngwen/gopher/humor
These are files! You can verify that by typing
ls -l ~pngwen/gopher/humor
Note, however, that these files don't have extensions. This is
the case of a lot of Unix files. Unlike windows, Unix doesn't
depend on file extensions. We sometimes use them, but we don't
have to. So how can we sort out what each file is? Well we have
to look inside it. There is a special command for doing this,
and that is the file command. Type the following command:
file ~pngwen/gopher/humor/geeks
Now you know that this is a text file. The file command
determines this by using a large database of "magic numbers"
which it matches against your files to tell you what they are.
11. So now you know that that's a text file. Would you like to look
inside? Of course! (Especially given that this is in the humor
folder, it might be fun!) So let's dump the file to your
terminal. To do this, type:
cat ~pngwen/gopher/humor/geeks
Enjoy!
12. Try a few of my other humor files out. You probably have noticed
that some are too large to fit on one terminal screen. Another
way to open them is using the "more" command. Try:
more ~pngwen/gopher/humor/threes
Read this file. It reveals something of your future... Note that
more stops the screen after each page full. Press space or enter
to scroll down.
13. What if you wanted your own copy of threes? Well, you could do
that using the "cp" command. Type
cp ~pngwen/gopher/humor/threes .
then list your folder. You now have your own copy of threes! So
what's that "." at the end about? Well cp has to have a
destination. You can specify either a file name or a directory.
"." means your current directory, so that copies it with the same
name to your current directory. You can also specify a new file
name. For instance, try:
cp threes threes2
Now list your folder. Now you have 2 copies of this wonderfully
depressing poem!
14. What good is two copies of a text file? Not much! Let's get rid
of the second copy. We do this with the remove command:
rm -i threes2
The -i tells it to question what you are doing. Unix is
remarkably obedient, so if told it to do something that was bad,
it would. The -i is for your safety, but if you are confident
you can leave it off.
15. Phew! There's a lot of commands! They have lots of little
switches and complex behaviors. How do we keep it all straight?
Well, in the beginning, you have to lean on the manual. The
manual has a complete reference of most of the commands that you
will be using. Often it tells more than you would ever need, but
it is a great reference nonetheless. Let's look at the manpage
for "ls". To do this, type:
man ls
This will tell you all about the ls command. Try it for a few
of the other commands we have used. Oh, and you may ask
yourself, is there a manpage for man? Yup! Try:
man man
How meta is that?
16. Man is great if you need to know all the switches to a command
when you know what the command is, but how about when you haven't
a clue about how to do something? Not to worry, man's got your
back! You can do a keyword search of man. Try:
man -k directory
This will show you all the commands/pages about directories.
There's a bunch of them! Try this:
man -k directory | more
That vertical bar is called the "pipe" symbol. You make this by
typing "Shift + \" which is right over the enter key. What this
does is take the output of man, and makes it the input of more.
Thus you can use more to page through the large input. Try a few
other topics, like "permissions" or "compile" or "debug". Enjoy
poking around!
Organizing Files
================
Now you can copy files, you can list them, you can use the manual,
and you are almost ready to move into harder labs. First, however,
we need to learn how to organize our files.
As mentioned before, we organize files into directories. This
section will guide you through using directories and how to turn in
your labs.
1. To make a directory, use the mkdir command. Each of your labs
will be in its own directory, so as to not make a big mess! So,
let's make one for the present lab:
mkdir lab1
2. To change directories, use the "cd" command.
cd lab1
You can also use cd to change to an absolute path. For instance,
cd ~pngwen
will dump you into my home directory. Try that now. ACK! How
do you get back to your home? Easy! Just type:
cd
with no arguments, and you go home. No slippers, no witches, no
little dogs. Just pure computer science. Ok, let's go back into
the lab1 folder.
cd lab1
Verify you are in this folder. (Remember the command to do
that?)
3. Let's copy all of my humor files into your home folder. You can
do this by typing them one by one. Or you can use a wild card:
cp ~pngwen/gopher/humor/* .
4. List your folder, read some of the files. Pick your favorites.
Welcome to the world of geek culture! I pulled these files off
the real Internet, back before the web took it all over. Some
even came off a BBS at 300 baud. Ah, the good old days! It was
all text back then. It was glorious!
Further Reading
===============
You've come a long way in a short time! Of course, we have only
scratched the surface of what you can do with the UNIX/Linux command
line. For additional reading, please see:
http://www.sdf.org
http://tldp.org/
http://tldp.org/LDP/intro-linux/html/index.html
Or just gaze into the raw Internet. It's largely powered by UNIX.
You'll gain a lot from looking into it. See sdf.org to see what the
Internet really is.
Copyright (C) 2013 Robert Lowe
This work is distributed under a Creative Commons
Attribution-ShareAlike 3.0 Unported License (CC BY-SA 3.0)
For more information, see
http://creativecommons.org
