Using the Command Line
Table of contents
Basic Command usage
Unix is primarily designed to be used via a terminal. This is also supposed to include getting help and documentation. Because web based documentation is out of the picture, most programs include help messages and manual pages. You can always consult those for help. This page will not cover how to navigate files and the file system in UNIX.
It is very hard to learn how to use something by reading a guide. Try these commands yourself.
Getting Help
The man pages
man is short for manual. The manual pages are divided into chapters, each of which explain how to use various parts of the system.
To close a man page, simply type q.
alias woman=man if you want to be funny.
Manpages don’t just give you documentation for unix commands, but also for standard C functions. If your VM didn’t automatically install them, you can use $ sudo apt install manpages to get them.
To read the manpages, you can use the command $ man <unix command name/C function name>. For example, $ man cd or $ man malloc. The manpages will give you a pretty in-depth explanation on what they do.
Here’s some of malloc’s manpage:
If you want to keep your terminal window free to work in, manpages are also available online.
echo
The echo command writes any text following it to the terminal
Try running echo hello
sudo
sudo is short for “Super User DO”. It is a way of running a command as the root user (administrator) without being logged into the administrator account. By default, the root account is disabled, and you can only access it by running commands with sudo.
To use the sudo command, your user account must be in the sudoers group. Your first user account will be in the group by default, any other accounts may not be.
sudo is dangerous. You can very easily wreck your whole VM if you use it wrong. Be careful when you type any command that starts with sudo.
To test the sudo command, you can run
sudo whoami
the whoami command returns the username of the account which ran the command. If you run whoami as sudo, you may notice that this will return root
On the other hand, if you run whoami, it will return your username, not root.
apt
Unlike installing software on Windows and Mac os, Linux uses a package manager. This is somewhat similar to an app store, except that everything is free, and it’s actually useful. The default package manager is apt on debian based systems, like ubuntu.
apt is a wrapper for apt-get. For most of your usage of debian based linux distributions (like ubuntu), you will want to use apt. Most features of apt must be run as sudo. This means you must run sudo apt update instead of apt update to avoid getting a permission denied error.
apt update
This checks for any available updates for your system. It does not install them. This updates the list of available software for your operating system.
apt upgrade
This will update any packages that need an update. You may need to restart to for some updates to apply fully, but for the most part, you don’t.
apt install
This allows you to get new packages. If you know the name of a package you need to install, you can use apt install <name> to install it on your computer. For example, if you want to install valgrind, you can type apt install valgrind. Remember that all of these commands must be run with sudo.
apt remove
This does exactly what you think it does. If you have installed a package, you can remove it using apt remove
Combining Commands
While all of these commands aren’t very powerful on their own, they become a lot more powerful when you can chain them together.
The pipe
the pipe (|) operator takes the output of one command and sends it to the next one. Tru running echo hello | xxd. You will get how to write “hello” in hex.
Running a commmand inside another
To run a command inside another, you can use the $ and parenthesis. For example, you can run `xxd
Redirects
Most commands in bash have some input and some output. You can ###