bleeprot(8) System Manager's Manual bleeprot(8)

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home writing fortunes library links

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Linux is an operating system (OS) just like Windows and MacOS are operating systems, but it differs in many ways.

The primary means of interacting with a Linux system is through the *shell* (there do exist graphical environments for Linux, but for our class we will work primarilly with the *shell*). Some folks refer to this as a *command-line* interface or a *terminal user interface* (this is a call-back to how user originally interacted with early computers...using a *terminal*). For this tutorial (and to avoid further confusion) I will use the *shell* terminology.

Working directly with an OS shell can be intimidating at first, but it just takes some practice. Follow along in this tutorial on your emulated system.

When you first boot-up and log into your system you should be greeted with the following text:

student@cs $

This is your *shell prompt* (it is prompting you for a command). You will enter commands and the OS will process commands exactly as you have entered them. There are a **lot** of commands, so the easiest thing to do is to just learn them as you go.

Each header in this tutorial will start with a list of commands and will then walk you through examples of how to use them.

* pwd - print working directory
* cd - change directory
* ls - list files / list directory contents

These commands are primarily used for navigation around the system. Something to keep in mind is that there is no 'desktop', so you are always 'in' a specific directory on the computer. When we first log into the system we have a location which can be given to us by the ‘pwd’ command.

student@cs $ pwd
/home/student
student@cs $

As you can see I am in my *home* directory ( ‘/home/student’ ). If I enter the ‘ls’ command the OS will list out the contents of the directory that I am currently located in (in this case ‘/home/student’ ).

student@cs $ ls
Desktop   Downloads builds    documents kicad     projects
student@cs $

There are other directories nested under my home directory. I can move into one with the ‘cd’ command (i.e. change directory to a new location).

student@cs $ cd documents/
student@cs $ pwd
/home/student/documents
student@cs $ ls
topsecretplans.pdf                      x86_vol1.pdf
Forthprimer.pdf                         x86_vol2.pdf
w65c02s.pdf                             x86_vol3.pdf
w65c22.pdf                              x86_vol4.pdf
student@cs $

In this example I used ‘cd’ to enter the ‘documents’ directory. Then, when I used the ‘pwd’ command you can see the OS showed me my new location ( ‘/home/student/documents’ ). Finally, I entered the ‘ls’ command and the OS listed the contents in that directory (a handful of PDFs).

The files on your system are stored in a nested tree structure called a file hierarchy. It looks like this:

Filesystem Hierarchy

Each directory has a specific purpose, but you will spend most of your time in your home directory. User home directories are located in ‘/home’ <my> examples my username is ‘student’ , so my home directory is ‘/home/student/’ All of my other personal directories are located within this one.

The path of a file is it's full location. For example, the path of my 'topsecretplans.pdf' file is ‘/home/student/documents/topsecretplans.pdf’ , and the path of the 'documents' directory is ‘/home/student/documents’

You can use ‘cd’ with a *relative* path or an *absolute/full* path. In my examples I was using ‘cd’ with a relative path (i.e. ‘cd documents’ changes to the documents directory which is in my home directory), but if I was in a completely different location and I wanted to change into that directory I could use: ‘cd /home/student/documents/’

* mkdir - make a directory
* mv - move a file
* rm - remove a file
* cat - concatenate files (also shows the content if used with a single file)
* nano - edit a file (nano is a simple text editing program)

These commands are pretty simple. Let's start in our home directory. Then use the ‘mkdir’ command to create a new directory called *projects*.

student@cs $ pwd
/home/student
student@cs $ mkdir projects
student@cs $ ls
Desktop   Downloads builds    documents kicad     projects
student@cs $

As you can see we now have a *projects* directory. ‘cd’ into it and if you ‘ls’ again you should not see any files (because the directory is empty). Then, enter ‘nano a_text_file.txt’ You should be greeted with the nano text editor open on a blank file. It should look like this (but without the extra text in the file):

nano Screenshot

The nano editor is incredibly simple. All of commands are listed on the bottom of the screen (the ^ symbol indicates the control key, so to quit from nano you would use Ctrl-x, or to save the file you would use the write-out command which is Ctrl-o). Type in the file a bit and then save the file and close nano. Now, you can use the ‘cat’ command to see the contents of the file:

student@cs $ cat a_text_file.txt
Here is some text in my file!
student@cs $

Really the ‘cat’ command is for concatenating files together, but it also dumps the content of a file so we can use it for a single file to just view the content. For now, just know that it is helpful for quickly seeing what is in a file.

The ‘mv’ command actually takes two arguments ( ‘mv <target_file> <destination>’ ). We also use it to rename files. In the following example we move ‘a_text_file.txt’ to ‘new_name.txt’

student@cs $ mv a_text_file.txt new_name.txt
student@cs $ ls
new_name.txt
student@cs $

The
‘rm’
command just deletes files.
student@cs $ rm new_name.txt student@cs $
poof! 

* cc - c compiler

Okay now we can get some programming. Let's start in our
‘projects’
directory, and create a new directory called
‘project0’
student@cs $ pwd /home/student/projects/project0 student@cs $
Use nano to open a new file called ‘main.c’ type in the simple program below, write the file, and close nano.
#include <stdio.h> int main(void) { printf("Hiya!0); return 0; }
student@cs $ ls main.c student@cs $ cat main.c #include <stdio.h> int main(void) { printf("Hiya!0); return 0; } student@cs $
Now we can use our c compiler to compile the code into a special file called an executable (i.e. a file that can be executed/run).
student@cs $ cc main.c student@cs $ ls a.out main.c student@cs $
We now have an executable file ‘a.out’ For historical reasons this is the default filename output from the c compiler. Finally, we can execute the file with ‘./’
student@cs $ ./a.out Hiya! student@cs $

This tutorial is tiny! This is only scratching the surface of what the shell is
capable of. The OS shell is actually a functional programming language and can
be used to program your OS. That being said, this introduction should be
sufficient for our class this year. Come back when you need a refresher. Here is
a summary of the commands covered:


* pwd - print working directory


* cd - change directory


* ls - list files / list directory contents


* mkdir - make (create) a directory


* mv - move a file


* rm - remove a file


* cat - concatenate files (also shows the content if used with a single file)


* nano - edit a file (nano is a simple text editing program)


* cc - c compiler
December 16, 2024