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Working with the command line

Most of our activities will be done using the Unix command line (aka, the Unix shell).
It is thus highly recommend to have at least a basic grasp of how to get around in the Unix shell.
We have put together some resources to refresh your Unix skills.

Basic tutorial #1

Before starting

Windows users: Open this online Linux terminal in a new window.
MacOS/Linux users: Launch the Terminal app on your machine.

Please note:

Things inside a box like this...

mkdir unix_shell
cd unix_shell

...represent commands you need to type in.
Each line is a command.
Commands have to be typed in a single line, one at a time.
After each command, hit the Enter/Return key to execute it.

Things starting with a pound/hashtag sign (#)...

# This is a comment and is ignored by the shell

...represent comments embedded in the code to give instructions to the user, make notes about the code, etc.
Anything in a line starting with a # is ignored by the shell.

We will be using different commands with different syntaxes.
Different commands expect different types of flags and arguments.
Some times the order matters, some times it doesn't.
If you are unsure, the best way to check how to run a command is by taking a look at its manual with the command man.
For example, if you want to look at the manual for the command mkdir you can do:

man mkdir

# You can scroll down by hitting the space bar or pressing ctrl+f
# Press ctrl+b to scroll up
# To quit, press q

Creating and navigating directories

First let's see where we are:

pwd

Are there any files here?
Let's list the contents of the folder:

ls

Let's now create a new folder called unix_shell.
In addition to the command (mkdir), we are now passing a term (also known as an argument) which, in this case, is the name of the folder we want to create:

mkdir unix_shell

Has anything changed?
How to list the contents of the folder again?

HINT (CLICK TO EXPAND)

ls

And now let's enter the unix_shell folder:

cd unix_shell

Did it work?
Where are we now?

HINT

pwd

Creating a new file

Let's create a new file called myfile.txt by launching the text editor nano:

nano myfile.txt

Now inside the nano screen:

  1. Write some text
  2. Exit with ctrl+x
  3. To save the file, type y and hit the Enter/Return key
  4. Confirm the name of the file and hit the Enter/Return key

List the contents of the folder.
Can you see the file we have just created?

Copying, renaming, moving and deleting files

First let's create a new folder called myfolder.
Do you remember how to do this?

HINT

mkdir myfolder

And now let's make a copy of myfile.txt.
Here, the command cp expects two arguments, and the order of these arguments matter.
The first is the name of the file we want to copy, and the second is the name of the new file:

cp myfile.txt newfile.txt

List the contents of the folder.
Do you see the new file there?

Now let's say we want to copy a file and put it inside a folder.
In this case, we give the name of the folder as the second argument to cp:

cp myfile.txt myfolder

List the contents of myfolder.
Is myfile.txt there?

ls myfolder

We can also copy the file to another folder and give it a different name, like this:

cp myfile.txt myfolder/copy_of_myfile.txt

List the contents of myfolder again.
Do you see two files there?

Instead of copying, we can move files around with the command mv:

mv newfile.txt myfolder

Let's list the contents of the folders.
Where did newfile.txt go?

We can also use the command mv to rename files:

mv myfile.txt myfile_renamed.txt

List the contents of the folder again.
What happened to myfile.txt?

Now, let's say we want to move things from inside myfolder to the current directory.
Can you see what the dot (.) is doing in the command below?
Let's try it:

mv myfolder/newfile.txt .

Let's list the contents of the folders.
The file newfile.txt was inside myfolder before, where is it now?

The same operation can be done in a different fashion.
In the commands below, can you see what the two dots (..) are doing?
Let's try it:

# First we go inside the folder
cd myfolder

# Then we move the file one level up
mv myfile.txt ..

# And then we go back one level
cd ..

Let's list the contents of the folders.
The file myfile.txt was inside myfolder before, where is it now?

We have so many identical files in our folders.
Let's clean things up and delete some files:

rm newfile.txt

Let's list the contents of the folder.
What happened to newfile.txt?

NOTE:

When deleting files, pay attention in what you are doing: if you accidently remove the wrong file, it is gone forever!

And now let's delete myfolder:

rm myfolder

It didn't work did it?
An error message came up, what does it mean?

rm: cannot remove ‘myfolder’: Is a directory

To delete a folder we have to modify the command further by adding the recursive flag (-r).
Flags are used to pass additional options to the commands:

rm -r myfolder

NOTE:

The following command also works, but only if the folder is empty:
rmdir myfolder

Let's list the contents of the folder.
What happened to myfolder?

Basic tutorial #2

The basic tutorial #1 above covered a very small part of what we need to know to navigate the Unix command line.
Depending on your level of knowledge, you might want to practice a bit more.
You can, for example, follow this nice tutorial set up by Mike Lee (@astrobiomike):

astrobiomike.github.io/unix

Command challenge

If you're feeling wise, why not put your Unix knowledge to test?

cmdchallenge.com