Unit 2: Making Things

Folders, files, copies and the delete key.

Unit 2 of 8 in Linux and the command line for kids. Its 7 lessons are New Folders, New Files, Reading a File, Copying, Moving and Renaming, Deleting and Tidy the Desktop — below is everything each one explains, and a question or two from it to try.

Every terminal session on this page was replayed before it shipped, on a machine whose every message is tested against real bash and coreutils.

This unit is free for ever, because the first two units of every track are. Try it in the app.

📁 New Folders

Make a directory

Linux calls a folder a directory. Same thing, older word.

mkdir makes one. Give it a name and it appears — no window, no dialog box, no "are you sure".

Terminal

kid@alguni:~$ mkdir photos
kid@alguni:~$ ls
photos

Several at once

Give mkdir more than one name and it makes them all. Most commands work like that: whatever you can do to one file, you can usually do to twenty.

That is the whole reason a terminal is worth learning.

Terminal

kid@alguni:~$ mkdir maths english art
kid@alguni:~$ ls
art
english
maths

When the way there does not exist yet

Ask for school/maths/homework when there is no school yet and mkdir stops: it will make one folder, not three.

-p means "make the parents too". It is the difference between a complaint and a whole path appearing at once.

Terminal

kid@alguni:~$ mkdir school/maths/homework
mkdir: cannot create directory 'school/maths/homework': No such file or directory
kid@alguni:~$ mkdir -p school/maths/homework
kid@alguni:~$ ls school
maths
kid@alguni:~$ ls school/maths
homework

Try it yourself

What does -p do for mkdir?

Makes every folder on the way there as well
Prints the folder it made
Protects the folder from deleting
Puts the folder in your home

Answer it in the app

📄 New Files

An empty one

touch makes an empty file. Nothing in it at all — just a name on the disk, waiting.

It is useful more often than it sounds, because plenty of programs only need the file to *be there*.

Terminal

kid@alguni:~$ touch diary.txt
kid@alguni:~$ ls
diary.txt

With something in it

echo says something back to you. On its own it is not very useful.

But > catches what a command was about to print and puts it in a file instead. That arrow is one of the best ideas in the whole system, and unit 4 is entirely about it.

Terminal

kid@alguni:~$ echo "hello there"
hello there
kid@alguni:~$ echo "hello there" > greeting.txt
kid@alguni:~$ cat greeting.txt
hello there

Adding instead of replacing

That is the trap: > throws away whatever was in the file.

>> adds to the end instead. One arrow replaces, two arrows add on. It is worth saying out loud a few times.

Terminal

kid@alguni:~$ echo "monday" > week.txt
kid@alguni:~$ echo "tuesday" >> week.txt
kid@alguni:~$ echo "wednesday" >> week.txt
kid@alguni:~$ cat week.txt
monday
tuesday
wednesday

Try it yourself

What does the last line print?

Terminal

echo "one" > count.txt
echo "two" > count.txt
cat count.txt

Answer it in the app

🔎 Reading a File

Concatenate

cat prints a file. Its odd name is short for concatenate, because it can print several files stuck together one after another.

That is what it was really built for. Printing one file is just the thing everybody uses it for.

Terminal

kid@alguni:~$ cat monday.txt
sausages
kid@alguni:~$ cat monday.txt tuesday.txt
sausages
pasta

Just the beginning, just the end

Some files are enormous. cat on a file with a million lines is not helpful.

head shows the first ten lines, tail shows the last ten, and -n says how many you actually want.

Terminal

kid@alguni:~$ head -n 3 numbers.txt
1
2
3
kid@alguni:~$ tail -n 3 numbers.txt
98
99
100

When the file is not there

Ask for a file that does not exist and cat says so, using the name you gave it.

Nine times out of ten that message means you are standing somewhere else than you thought. pwd and ls are the fix.

Terminal

kid@alguni:~$ cat homework.txt
cat: homework.txt: No such file or directory

Try it yourself

What does this print?

Terminal

head -n 2 letters.txt

Answer it in the app

📑 Copying

From, then to

cp copies. It always takes two things: what to copy, then where to put it.

That order never changes, in cp or in mv. From first, to last.

Terminal

kid@alguni:~$ cp story.txt backup.txt
kid@alguni:~$ ls
backup.txt
story.txt
kid@alguni:~$ cat backup.txt
chapter one

Into a folder

If the last thing you name is a folder, the copy goes inside it and keeps its name.

That is how you copy several files at once: name them all, and put a folder last.

Terminal

kid@alguni:~$ cp a.txt b.txt backups
kid@alguni:~$ ls backups
a.txt
b.txt

Copying a whole folder

Try to copy a folder and cp refuses, because copying a folder means copying everything inside it and it will not assume you meant that.

-r means recursive: go in, and keep going in. You will meet -r again on the command that deletes, where it matters a great deal more.

Terminal

kid@alguni:~$ cp project copy
cp: -r not specified; omitting directory 'project'
kid@alguni:~$ cp -r project copy
kid@alguni:~$ ls copy/notes
plan.txt

Try it yourself

What does cp -r do that plain cp will not?

Copy a folder and everything inside it
Rename the copy
Copy the file twice
Replace a file without asking

Answer it in the app

🚚 Moving and Renaming

One command for two jobs

mv moves a file into a folder. Same shape as cp: from first, to last.

The surprise is that there is no rename command — because renaming is just moving without going anywhere. Move old.txt to new.txt and you have renamed it.

Terminal

kid@alguni:~$ mv untitled.txt rocket-plan.txt
kid@alguni:~$ ls
plans
rocket-plan.txt
kid@alguni:~$ mv rocket-plan.txt plans
kid@alguni:~$ ls
plans
kid@alguni:~$ ls plans
rocket-plan.txt

Names with spaces in them

The shell splits what you type at every space, so my homework.txt looks like two things to it.

Put quotes round a name with a space in it and the shell keeps it whole. This is the first hint that the shell is a language with rules, which is where unit 7 goes.

Terminal

kid@alguni:~$ touch "my homework.txt"
kid@alguni:~$ ls
my homework.txt
kid@alguni:~$ mv "my homework.txt" homework.txt
kid@alguni:~$ ls
homework.txt

Try it yourself

How do you rename cat.txt to dog.txt?

mv cat.txt dog.txt
rename cat.txt dog.txt
cp cat.txt dog.txt
mv dog.txt cat.txt

Answer it in the app

🗑️ Deleting

There is no bin

This is the one to be careful with. rm removes a file, and there is no recycle bin to get it back from. It does not ask. It just goes.

That is not the terminal being cruel. It is the terminal doing exactly what you said, which is what you want the rest of the time.

Terminal

kid@alguni:~$ ls
keep.txt
rubbish.txt
kid@alguni:~$ rm rubbish.txt
kid@alguni:~$ ls
keep.txt

Empty folders

rmdir removes a folder, but only if it is empty. That refusal is a safety catch, not a nuisance: it is the computer checking you know what is in there.

Terminal

kid@alguni:~$ rmdir empty
kid@alguni:~$ rmdir full
rmdir: failed to remove 'full': Directory not empty
kid@alguni:~$ ls
full

The dangerous one

rm -r deletes a folder and everything inside it, all the way down, without asking once.

It is genuinely useful and it is how people lose a year of work. The habit that saves you is boring and it works: run ls on the folder first, and read what comes back.

Terminal

kid@alguni:~$ ls old
notes.txt
pictures
kid@alguni:~$ rm -r old
kid@alguni:~$ ls

Try it yourself

You type rm -r photos and press enter. What happens?

photos and everything in it is gone, with no way back
It asks you first
It moves photos to the recycle bin
It refuses, because photos is not empty

Answer it in the app

🏆 Tidy the Desktop

A real job

Somebody has dumped fifteen things in one folder. Photos, homework and rubbish, all mixed together.

You have everything you need: mkdir, mv, rm, and ls to check as you go.

Try it yourself

Which of these can you not undo?

rm -r photos
cp photos backup
mkdir photos
ls photos

Answer it in the app