Command-line

Abbreviations

*[CLI]: Command Line Interface
*[WSL]: Windows Subsystem for Linux

Introduction

In this subunit, we'll introduce you to the Command-line, how to navigate with it, and create folders in it. The most essential part of working with the Terminal is knowing how to navigate around within it. We'll start by teaching you some essential commands like ls, mkdir, pwd, and cd so you can always know where you are and move to where you want to go.

When you're starting to visualize how the Terminal and command line work, think about finder or Windows explorer. You use these tools to navigate through the files, folders, and directories on your computer—and to open things like applications. The Terminal and command line offer you another way to explore these files and directories; through commands you type. The functionality you get from the Terminal is far more powerful and robust—for instance, you can push your entire codebase to GitHub with one line... or pull down any updates that have been made. We'll explore how to do this in the next unit.

Terminal Introduction

Goals

Define what Terminal is and how it is structured
Navigate through and list files on your machine
Define the following terms: shell, terminal, directory, absolute path, relative path
List files using flags
Create, move, copy and remove files
Explain what the following commands do: cat, echo, less, open

What is Terminal

Terminal is an application that gives us a command line interface (CLI) to interact with the computer.

Everything you can do in Finder or Windows Explorer, you can do in the Terminal, but it's faster!

What is a shell Bash/ZSH

You will also hear the term "shell" when learning about Terminal, so it is important to distinguish between these terms.

shell: the program which actually processes commands and returns output

Most shells also manage foreground and background processes, command history, and command line editing.

These features (and many more) are standard in bash, the most common shell in modern linux systems

terminal: a wrapper program which runs a shell

Decades ago, this was a physical device consisting of little more than a monitor and keyboard.

As unix/linux systems added better multiprocessing and windowing systems, this terminal concept was abstracted into software.

Installing Terminal

If you're on a Mac or Linux, you're good to go! Launch the Terminal application

If you're using a Windows machine, we recommend using Git Bash

There are other options for installing a Terminal on Windows; however, the most user-friendly option for this course is Git Bash. If you choose to use another option like WSL, that is totally

Path and Folders

In the Terminal, all files and folders begin at the root directory

The root directory is noted by a /.

Inside the root directory are essential files/folders that your machine needs, but we do not modify the files and folders in the root directory often.

The users folder

Inside the root directory, we have a folder called Users which contains all the user accounts on your computer.

If you move into the directory for your user account, you will be in the home directory, which is denoted by ~.

For example, if your username on the computer is colt, then your home directory would be /Users/colt.

A synonym for the /Users/colt path is ~ when you are logged in as colt.

Moving Around

The first thing you want to start to understand when using the Terminal is how to navigate from folder to folder.

Where am I

Before you start moving around, it’s helpful to know where you are.

Thankfully, there is a handy command called pwd which will display the absolute path and let you know what current directory you are working in.

So if you are ever unsure, just type in pwd (which is short for print working directory).

Moving around

One of the most common commands you will be using in the Terminal is cd which is short for “change directory.”

In order to change a directory, type cd followed by the directory or a path to the directory.

If we want to move up a directory, we use cd .. and if we want to move into a directory, we specify the name of the directory we are moving into.

For example, if you are in your home directory and type cd Desktop, you should move into your Desktop directory.

We just mentioned that you can type cd followed by a directory or path. But what is a path?

Absolute Paths vs Relative Paths

A path is simply the way to reach a file or folder; it's like an address for the file or folder you're trying to reach.

When we specify a path starting from the root directory /, we call that an absolute path.

If you’re currently in the ~ home directory, and you want to change directories into the Desktop folder, here are two following ways:

cd Desktop - relative to where I am currently
cd /Users/colt/Desktop - absolute, starting from the root (first /, then Users, then colt, then **Desktop **)

Moving around the terminal efficiently

One of the hardest parts about getting used to the Terminal is the handling an interface where you cannot easily use a mouse!

This means we will have lots of typing to do and quite a few shortcuts to learn!

If you hold down the alt/option key, you can click on a line in the terminal to move your cursor there, but it is still much easier to get comfortable with keyboard shortcuts

Useful keyboard shortcuts

Command/Control + a (move to the beginning of line)
Command/Control + e (move to the end of line)
Command/Control + w (delete the word where your cursor is)
Command/Control + u (delete an entire line)
Option/Alt + left/right (jump between words)

Command-line Cheatsheet

Listing Files

One of the most important commands you are going to be using is ls, which lists the contents of a directory.

Typing ls in your home directory will show you all the files and folders inside that directory.

Sometimes the default ls command does not give us all the information we want. In such cases, we'll need to add some flags to get more details.

Flags

Flags can change and even enhance commands and are added using a - after the command.
Flags are usually represented by single uppercase and lowercase letters.
With the ls command, we can pass in the - a flag to list "all" files (including hidden files and folders).
If we want the ls command to give us more information about each file, we can pass in the -l flag.
To combine flags, we can just use one - and pass in each flag. So the command to use ls and show all files and more detailed information about each one would be ls -la.

Using flags for ls will be essential when working with permissions as well as when you start working with * * git**.

Using the manual to learn more

If you ever want to learn more about a terminal command, you can use the man command followed by the terminal command to see a manual on the command!

Let’s try it with ls

man ls

Files and Folders

Creating Files And Folders

To create a folder, we use the mkdir command (short for “make directory”), followed by the name (or space-separated names) of the folder(s) that we would like to create.

mkdir first_folder

Now that we made the first_folder, how do we change directories into it?

We use the cd command!

Now that we are inside our new folder, first_folder, let's create a new file. A simple way to create a file is with the touch command.

touch first_file

Displaying the Contents Of A File

You can display the contents of a file using the cat command.

If you type cat NAME_OF_FILE, you can see the contents of the file easily, right there in the Terminal.

Let’s add some text to a file so that we can use cat.

echo "Hello World" > first_file

The echo command simply writes text to the terminal.

The > is called a redirect. The > redirects the output from the command on the left side into the file on the right-hand side.

We will see more on redirection later on!

Opening up a file

If you would like to open up a file, you can use the open command.

So if we want to see the contents of first_file we can do open first_file.

The open command is also very useful if you want to open all the files and folders in a directory.

Moving Files And Folders

To move files and folders, we use mv command. Let's try this out!

mv test.txt ../

Renaming files and folders

mv test.txt newfile.txt

Copying Files and Folders

Sometimes you may want to make a copy of a file or a folder. To copy a file, we use the cp command (short for copy).

cp PATH_TO_ORIGINAL_FILE PATH_TO_COPIED_FILE

For example, if we wanted to create a copy of test.txt and call it test_copy.txt, we could enter the following command (assuming we’re inside the first_folder):

cp test.txt test_copy.txt

In order to copy a directory, you need to modify the cp command as follows:

cp -r first_folder first_folder_copy

The -r is called a flag; you can think of a flag for a command as an option that can be passed to that command.

To learn more about the flags that you can pass to cp, you can type man cp.

Deleting Files And Folders

To remove a file or a folder, we use rm command.

rm newfile.txt

If this works, you should not see any output from the Terminal. You can always run ls make sure the file is not there

Where did it go?

Now that it is gone… where did it go? The Trash? The answer is it is completely removed from your computer.

There is no undo so be VERY careful when using the rm command.

Removing a folder

It turns out that rm is for a file, while the command rmdir is used to remove (empty) directories.

If there is anything inside the folder, you will have to use rm -rf.

Like we saw with cp, the r and f in -rf are examples of flags

Last modified: 10 March 2024