Command Line Interface

Why is this important?

This workshop is important because:

Most people are familiar with their computers' graphical user interface, rich with icons and buttons. The command line interface, or CLI, is an alternative without these fancy graphics -- a plain, text-­based interface for performing tasks on a computer.

Many of the tasks developers perform are faster when done from the command line, and the command line interface usually has some extra features that are hidden in normal graphical interfaces. That's because programmers assume someone using the command line is more knowledgeable about their computer and less likely to make mistakes. Think about that from an employment perspective, too. As a developer, you will be expected to be proficient with your computer, including performing basic tasks on the command line.

What are the objectives?

After this workshop, developers will be able to:

• Navigate the file system from the command line.
• Create, move, copy, and delete files or directories from the command line.
• Research unfamiliar shell commands with --help, man, and/or online resources.
• Describe the uses of the sudo and chmod commands.

Where should we be now?

Before this workshop, developers should already be able to:

• Open a command line interface on a computer (Terminal in Mac).
• Accurately type commands into the command line interface.
• Find absolute and relative file paths.
• Navigate the file system from the graphical user interface.
• Create, move, copy, and delete files or directories from the graphical interface.

What is the Command Line Interface?

• A CLI is a program to interact with a computer through text. Mac's command line "shell" program is called Terminal. It lets users interact with the operating system. It's a "Read, Evaluate, Print, Loop"-style program.

  You do: Try using the keyboard shortcut Command Space to search for "Terminal". Open Terminal.

• User can input commands in a specific "shell" scripting language. The default command line language for macOS and many Linux distributions is called bash. You may also eventually use variants like zsh, ash, ssh, and their predecessor sh.

  You do: In Terminal, use the bash command pwd. What does it tell you?

Check for Understanding

1. Write down three tasks you have used Terminal for in the past.

2. Write down bash commands for each of the tasks you thought of.

Hint: If you're having trouble figuring out how to do something in the Terminal, try searching online for that task plus "in Terminal" or "in bash":

• "create a file in bash"
• "list hidden directories in bash"

Note: git commands are not part of the bash language. They use bash, and they're added separately when you install git.

Bash Commands

Commands on the command line work a lot like functions in JavaScript. The base command is often followed by some number of arguments, and/or by some options or flags.

For example, let's take the command git add. This isn't a built-in part of bash; it's an extra command that we'll use quite often to have git make a record of changes.

Here's how we might use git add:

git add ./styles --all

The main command here is git add.

Next, there's a relative file path for a directory: ./styles. That's the target of the command. You can think of it like an argument to the git add function.

Then, there's a --all flag. Flags are special options that make it easier to customize how a command behaves. For git add, --all tells git to record the fact that we deleted some files.

Note: While the main command must always come first, you can often put flags before or after the other arguments. Pay attention to the documentation for a command to see how it can be used.

Getting more information about a command:

1. man

2. --help

3. Online searches (try adding "in bash" or "Terminal" to your search).

You do: Practice using the resources above - to define each of the essential commands and common flags below!

Essential Commands

0. man

1. cd

2. ls

3. mkdir

4. touch

5. mv

6. rm

7. cp

8. which

Common Flags

The same flags won't work with every command, but knowing a few will help you decide what to look for in a new command's documentation.

1. -r, as in cp -r and rm -r

2. -a, as in ls -a

3. -f, as in rm -f

4. --help, as in git --help

5. --version, as in ruby --version

Important Locations on the Mac

Absolute Paths:

/ (root directory)

/ is the computer's root directory, which contains all the files on the computer.

~ (home directory)

~ is the home directory for the current user. In Finder, it's named with your user name. You can ls ~ to see everything inside it - things like Desktop, Documents, Downloads.

• You do: In Finder, press CMD SHIFT H to enter your home directory. Then press CMD ArrowUp to go one directory up, to the Users directory. Find the home directory with your user name, and drag it into your favorites so it's easy to find later!

Relative Paths:

. (current directory)

. is the current directory. It's sometimes used for commands that require a location. For example, cp ~/Downloads/kitten.png ./ copies the kitten image from the downloads directory into the current working directory.

• You do: What would cd . do? Try it out and see if you were correct!

.. (parent directory)

.. is the directory containing whichever directory you're in, known as the "parent" directory. It's often used when navigating files: cd ../.. would move you two levels "up" the file tree.

Tab Completion

When you're typing a file or directory name, you can hit Tab as soon as you've given the computer enough information to know which file you need. Try it!

$ cd ~   
$ ls  
Desktop Documents Downloads
$ cd D    # if you hit Tab after D, you may hear a beep - the computer can't tell which directory you want yet.
$ cd De   # now Tab will fill in Desktop

Commands for permissions:

1. sudo: run a command as another user, usually the "super user" with significantly more permissions. Make sure you understand the effect a sudo command will have before you run it and that you trust its source. See the man page and/or wikipedia.

2. chmod: change which users and groups have permission to access a file or direcotry. Use with care. See the man page and/or an explanation.

Closing Thoughts

Review!

1. What is bash?

2. What is a "shell"?

3. What will be your go-to resource to learn about an unfamiliar command?

Put it into practice!

New commands and shortcuts will take a while to get used to. Practice with them to get more comfortable and more efficient working with your computer.

1. When you need to work with your file system in WDI, use the command line. Build a habit of using cd, ls, mkdir, and touch.

2. Another important part of using your computer efficiently is learning keyboard shortcuts. Get used to using Command Space to open spotlight for searching, Command Tab to switch between programs, and Command F to find a phrase in a program you have open.

If you're already comfortable with the Terminal commands and shortcuts listed above, choose three from the resources below to start focusing on. Write these down on a sticky note, and stick it inside your laptop or somewhere that will help you remember to use them.

Additional Resources

1. Terminal Commands
2. Mac & Atom Keyboard Shortcuts