The Command Line Interface

Objectives

• View files within a directory.
• Create a directory (folder) to store a project.
• Create subdirectories to organize a project.
• Create files to hold project information.
• Edit and delete files.
• Navigate within a project.
• Get help from user manuals.

Introduction to the Bash Terminal

What is a Bash terminal? It is a tool that allows us to interact with our computer using commands. Normally, we interact with our computer through a program's interface, such as a file explorer application. However, the terminal provides an alternative way to interact with our computer.

To open your file explorer application, you can click on its icon. Take note of the files you see there.

Note: On Mac, new windows don't open to the Home directory by default. To find this directory, click on "Go" and then "Home" at the top left of the computer screen.

Exploring the Home Directory

When you open your terminal, you will notice that you start in your Home directory by default. You can see the files in this directory by using the ls command (mnemonic: "list"). The files and directories listed in the terminal will be the same as the ones in the file explorer application.

So, the terminal provides an alternative way to interact with our computer.

User Manuals

The terminal offers commands that allow us to interact with it. Fortunately, the terminal also comes with a manual that provides information about these commands.

To access the manual, use the man command followed by the name of the command you want to learn more about. Let's see how this works.

Inside your terminal, type the following command:

man rm

You will receive the following information:

NAME
     rm, unlink -- remove directory entries

SYNOPSIS
     rm [-dfiPRrvW] file ...
     unlink file

DESCRIPTION
     ...
     The options are as follows:
     -d Attempt to remove directories as well as other types of files.
     ...

Let's break down each section on this manual page:

• Name: The name of the command, followed by a brief description of what it does.
• Synopsis: A formal description of how to run the command and what command line options it accepts.
• Description: A textual description of how the command works.

In the Synopsis section, you can see how to use the rm command. Let's use this information to remove a directory called "removeMe":

rm -d removeMe Here's the breakdown of the command:

• Start with the command, rm.
• Use the option or flag, -d, because this is a directory. By default, the rm command only removes files.
• Provide the name of the directory you want to remove. Note: In the Synopsis section, you see [-dfiPRrvW]. These are commonly called flags. You can find the description of each flag in the Description section of the manual.

Cheat Sheet

Group Activity

Let's familiarize ourselves with some common commands and create a cheat sheet for reference throughout this lesson. Open cheatSheet.md and complete each section. We already went over rm so it's already completed for you.

Exploring the File System

You're probably used to creating files and folders using your operating system's "explorer" program. The common explorer programs found on each OS are:

Mac: Finder Windows: File Explorer Ubuntu: Files On unix-like systems (sometimes referred to as *nix or POSIX), all your files are stored in your home folder. On Windows, your files are usually stored in "My Documents".

You might see ~ or $HOME used to refer to your home folder on unix-like systems.

Directories and Paths

Directories (and subdirectories) are typically referred to as "folders" in your file explorer. They serve as convenient ways to group files together. Paths are textual representations of your current location in the file hierarchy or "tree".

Examine this path: /Users/Zomia. The leading slash (/) represents the root of the file system. The "Users" part indicates the presence of a directory (or folder) named "Users" within the root of the file system. Inside the "Users" directory, there is another directory called Zomia. Therefore, the string /Users/Zomia is an absolute path to the home directory of the current user.

Absolute Paths

An absolute path provides the unique location of files and directories within the file system. No other files can have the same absolute path.

Note: It can be helpful to think of the path as the full name of the file, especially when moving or renaming files from the command line.

Absolute paths:

• Always start with a leading slash, '/'.
• Are relative to the root directory of the file system.
• The root directory is the highest-level directory in the file system's tree structure. When we refer to absolute paths, we are considering paths relative to the topmost path of the file system.

Explore the Root Path

Group Activity

In your terminal session, determine your current directory by using the pwd command (mnemonic: "print working directory"). What is the topmost directory in this path? What is the root of the file system?

Open the Finder and navigate to the root directory of your file system. You can do this by using the ⌘ + ⇧ + g shortcut in Finder, typing / and clicking Go. Take a look at the contents of the root directory.

Now, back in your terminal, change your current working directory to the root of the file system using the cd command (mnemonic: "change directory"). What happens if you type cd and then press the "Return" or "Enter" key? Let's wait before answering that question.

To change to the root directory, type cd /. In this case, we are providing the cd command with an absolute path. You can confirm that you are in the root directory by using the pwd command.

To return to your home directory, you can type cd ~, cd $HOME, or simply cd. Give it a try!

Relative Paths

Relative paths are paths described in relation to the current working directory. To determine the current working directory, we use the pwd command.

For example, if I'm in my home directory and I see a folder named "projects" (how would I see that?), I can guess that the full path to the "projects" folder is /Users/Zomia/projects. However, since I'm already in the home folder, the ls command only shows me the unique part of the name that distinguishes it from other sibling directories. Sibling directories are directories that exist beside other directories, rather than within them (child directories) or above them (parent directories).

This "partial path" is a relative path. It is quite useful because I can use it to change into the directory by using the cd projects command. So, in addition to accepting absolute paths, the cd command can also take relative paths to navigate through the file system. Pretty cool!

There are two special relative directories.

• .. represents the parent directory.
• . represents the current directory.

So, in order to navigate to a grandparent directory (parent of a parent) from the current directory, we would use the command cd ../...

Tab Complete

File paths can be long and typing them manually can be time-consuming and error-prone. Luckily, your terminal has a feature called tab completion that helps you fill in file and directory names. It works similar to autocorrect on a smartphone, but you need to press the tab key to trigger it.

Tab completion works with both relative and absolute paths. For example, if I have a file named a-very-very-long-filename.txt in my current working directory, I can type a-v (the first few letters of the filename) and press tab, and it will complete the filename for me.

Let's say I want to type the absolute path to that file, which is /Users/Zomia/trainings/a-very-very-long-filename.txt. I can do that quickly with tab completion! I could type /U, then press tab, then G and tab again, then t or tr and press tab, then a-v or a-, just like above.

Not only is this faster, but it also helps you verify if the file or directory you're looking for actually exists, preventing common mistakes. If you try to tab complete a non-existing file or directory, nothing will happen. So, whenever possible, make use of tab completion!

Make a Subdirectory

Group Activity

Now that we're back in the home directory, let's create a place to store all the work we'll do in this course. Naming can be challenging, but simple names are best.

Before executing the command in the terminal, bring your explorer window into focus, the one with the home directory open. Resize and position it so that it's visible alongside the terminal. Now, in the terminal, use cd to navigate to your Home directory.

Use the mkdir command to create a new directory called web-dev.

Create the following directories as well. They should be subdirectories of web-dev:

• practices
• projects
• tmp
• challenges
• studies

Verify that your directory structure resembles the following:

~/web-dev
├── challenges
├── projects
├── studies
├── practices
└── tmp

Now that we have our web-dev directory set up, let's use the mv command to move some files into it.

Find where the command-line and local-setup directories are stored (they may be in the Desktop directory). Then move those directories into the trainings directory.

Files

Let's use the tmp directory to experiment. tmp directories are conventionally used to store files that can be safely deleted. You should never put anything in them that you want to keep.

Create/Edit a File

Group Activity

Move into the tmp directory inside web-dev. Create a new file using the touch command. Let's create a blank text file named name.txt: touch name.txt.

Next, open that file in VSCode: code name.txt. Write your name inside this file and save it. On a Mac, the shortcut to save a file is ⌘ + s, or ctrl + s on Linux. You can also search for the save command (or any command) using the command palette. Try it by bringing up the palette with ⌘ + ⇧ + p (ctrl + shift + p on Linux). Then search for "Save".

Let's quickly take a peek inside the file we just created in our terminal. Type cat name.txt.

Now type open name.txt (xdg-open name.txt on Linux).

See what happened? The file name.txt opens in the default application your computer uses for that file type.

Let's say that we didn't mean to name the file name.txt. How would we go about editing the file name to correct it?

Copying a Hidden File

Bonus Topic: Group Activity

Hidden files in your file system are denoted by a leading dot (.). You can see these files using the command ls -a. Create a hidden file named .env. Copy this file to a new file named .newEnv using the command cp <original_name> <new_name>. Check your work by typing ls -a.

Deleting a File

Bonus Topic

How do we get rid of this file? We'll use the rm command. But first, a warning. This is a very dangerous command. Do not press enter after typing rm without being absolutely certain you're targeting the right file. There's no way to recover files deleted with rm. The same advice applies double to flags like -r or other flags. Flags are options that occur after dashes when issuing commands.

To delete a file or directory, use the following command:

rm -r <file_or_directory> # Will delete all files inside a folder as well as folder

Delete a File

Group Activity

Read the manual entry for rm. When you're done reading, you can quit by pressing q. Delete the name.txt file you created in the previous exercise. Type the command, then check with a colleague before pressing issuing the command.

#Important Note: Closing Your Terminal# You shouldn't close your terminal by clicking the "X" button. This can leave processes from that terminal session running in the background which can cause problems in the future. Instead, you should use a keyboard shortcut to safely and completely end the terminal session.

On macOS you should first press CTRL + D in any tabs that are running continuous processes like servers, then press CMD + Q.

On Ubuntu you should use CTRL + D. Note that this only is only possible when no process is running in the terminal -- you can end almost any process and clear any entered text with CTRL + C.