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Terminal 101 - The Basics
25 Apr 2017
6 minutes read

Most developers out there prefer to use a Command Line Interface (CLI) over the usual Graphical User Interface (GUI) for various reasons, the most common ones being:

  • It’s (usually) faster to use the CLI rather than the GUI;
  • You don’t need to move your hands away from the keyboard (to reach the mouse);
  • You can combine multiple CLI commands;
  • When working on a remote server, we often don’t have access to a GUI;

It does seem scary and challenging the first time you look at it, but as soon as you get the gist, you’ll see it’s not much different than using the normal interface.

Let’s start by defining what a command actually is. A command is nothing more than an instruction given by the user telling the machine to do something, such as listing the files inside a directory or deleting a directory. Commands are (most of the times) issued by typing them in at the command line (the terminal) and then pressing the (enter) key, which passes the command to the shell.

Shell is the program that receives the command and actually executes it. On most Linux systems (including on Mac OSX), the default shell is the bash shell.

Most commands also accept a pre-defined set of options, known as flags, that can be passed in to change the default behaviour of the command. A flag is usually a single letter or words prefixed by a dash (-). For example, the rm command is used to remove a file and, by default, doesn’t ask for user confirmation; if used in conjunction with the -i, it will ask for confirmation before actually deleting the file.

With these concepts defined, it’s time to finally open your terminal!

Choosing a Terminal

Unix machines usually come with a pre-installed terminal software. On Mac OSX, You can open it by pressing +space (on Linux, Alt+F2), typing “Terminal” on the box followed by .

TIP: The default terminal on OSX is quite simplistic. I recommend using ITerm2 instead.

With your terminal open, it’s time to start firing some commands!

Basic Commands

TIP: To read the man page of a command, try typing man command+. For example: man ls.

ls - List Directory Contents

Syntax: ls [target].

TIP: when you see square brackets in a command syntax description (such as in the ls [target] above), it means that [target] is optional.

To list the contents of a directory, type ls + in your Terminal window (from now on, I’ll omit the enter key after the command). You should see the files that exist in your HOME directory (more on HOME later). To see a detailed list, you can execute ls with the -l flag, that is, ls -l.

ls command

You can also specify a directory after ls, to get the list of contents of the directory (for example, ls Downloads will show the files inside the Downloads directory).

cd - Change Directory

Syntax: cd target.

To change directories, type cd followed by the name of the directory you want “cd” in, for example, cd Downloads.

TIP: Use the TAB to auto-complete the name of the directory; For example, if you type “cd Down” and press TAB, the shell will auto-complete to “cd Downloads/”

When you open a new terminal window, you’re (usually) in the HOME directory. You can go back to HOME at anytime by typing cd $HOME or cd ~. To go back to the previous directory you were in, use cd -. You can go up one directory by using .. as the directory name.

It is possible to combine directories and change to a subdirectory directly. For example, if you have the following directory tree:

HOME/
└── dev/
    └── onionworks/
        ├──foo/
        └── bar/

You could navigate the tree with the following commands:

cd dev/onionworks/foo   # HOME/dev/onionworks/foo
cd ..                   # HOME/dev/onionworks
cd bar                  # HOME/dev/onionworks/bar 
cd ../../               # HOME/dev
cd ~                    # HOME

cd command

mkdir - Make Directory

Syntax: mkdir name.

To create new directories, type mkdir followed by the name of the directory you want to create, for example, mkdir newdir. You can use the -p flag to create multiple subdirectories at the same time.

mkdir command

cp - Copy Files

Syntax: cp source destination.

To copy files around, type cp followed by the file you want to copy and the place you want the file to be, for example, cp Downloads/image.png Pictures/. If the last argument is a directory (like the example), the file will be copied to that directory; otherwise, a new file with the provided name will be created.

cp image.png Pictures/      # will copy to Pictures/image.png
cp image.png new_image.png  # will copy to new_image.png

You can copy multiple files using the * symbol:

cp Pictures/* Downloads/

By default, cp will now copy subdirectories. To include subdirectories, you can use the -r flag:

ls Pictures/
> image.png folder/ 
cp -r Pictures/* Downloads/
ls Downloads
> image.png folder/

cp command

mv - Move Files

Syntax: mv source destination.

While cp copies the file – i.e., creates a new file into the destination that has the same contents as the file on source, mv will move the file (or directory) from source into destination – i.e., the original source file will no longer exist after a successful mv.

TIP: you should use mv if you want to rename an existing file

mv command

rm - Remove Files

Syntax: rm target.

You can delete files using rm. Note that, by using rm, the file will be deleted and forever gone – it will not be moved to a “Trash bin” where you can later restore.

By default, rm will remove files only. Similarly to cp, you can use * to match multiple files. For example, to remove all png files from the Downloads directory, one can type: rm Downloads/*.png.

If you want to be prompted to confirm the deletion, add the -i flag. To remove all files, including subdirectories and its contents, use the -r flag.

rm command

Conclusion

It takes some time to get used, but you will soon find that it’s much faster to use the CLI than the GUI, but don’t worry! It does get easier from here and will soon retire your Finder/Explorer window in favour of a terminal. When you get comfortable navigating with the CLI, ensure to explore the man pages of the commands – each command has a lot more flags than the ones explained here. Check back soon for more terminal tips!


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