The Command Line

By the end of today

• Open a terminal without flinching
• Find your way around your own files
• Create, copy, move and delete things
• Read a command and guess what it does
• Get yourself unstuck

Cheatsheet at the end.

Who has opened a terminal before?

What is a terminal?

A place to type what you want,
instead of clicking it.

a different way to interact with your computer and/or files

It is not a seperate, parallel computer

Everything we do in the terminal can be seen in your filesystem.

Why terminal?

• Precise — "rename these 400 files" is one line
• Repeatable — you can save it and run it again
• Shareable — a command can be pasted in a message; a screen recording of clicking, is not as easy
• AI — your favourite agent uses it to do its work
• Everywhere — servers, phones, fridges, everything

Also, you get to feel like a hacker!

Getting a terminal

Opens a black-ish window with a blinking cursor

If you want to practice in a safe environment

https://cmdbox.hackenshaw.com/t/

Reading the prompt

anna@laptop:~/Documents$
 |      |        |      |
 you    machine  where  your turn

The $ means waiting for you.

Yours will look different. That is fine — every prompt is customisable, and it does not change what the commands do.

Terminal rules

1. Nothing happens until you press Enter
2. Case matters — ls is not LS
3. Spaces matter — they separate the words
4. There is no "are you sure?"

Don't be scared, just be aware of what you are doing.

(this is also good life advice)

First contact

READ THE ERRORS!

Three important questions

1. Where am I?
2. What is here?
3. How do I move?

Three commands to answer these questions...

Where am I?

pwd

print working directory.

"Directory" is just the old word for folder. You will see both.

What is here?

ls          # list what's in this folder
ls -l       # long: size, date, permissions
ls -a       # all: include hidden files
ls -la      # both at once

Words starting with - are options. They change how a command behaves.

How do I move?

cd Documents    # go into Documents
cd ..           # go up one level
cd ~            # go home
cd -            # go back where I just was
cd              # also home

change directory.

Shorthands

These work almost everywhere a folder name does, not just with cd.

You don't need to remember all of this.

Look it up 10 times then you will remember it (maybe).

Two kinds of path

cd Documents/notes

cd /home/anna/Documents

Starting with a / means it is an absolute path.

Getting around

Try relative and absolute paths

Two keys that will make your life easier

Tab completes what you are typing (if possible).
It is how you check you typed it right.

Looking inside files

cat notes.txt      # dump the whole file
less notes.txt     # scroll it - press q to quit
head notes.txt     # first 10 lines
tail notes.txt     # last 10 lines
wc -l notes.txt    # how many lines?

q quits less.

Reading things

Making things

mkdir practice           # make a folder
touch notes.txt          # make an empty file
cp notes.txt backup.txt  # copy
mv notes.txt final.txt   # rename
mv final.txt practice/   # ...or move

mv does both jobs. Renaming is moving, as far as the computer is concerned.

Removing things

rm notes.txt        # delete a file
rm -r oldfolder     # delete a folder and everything in it

Wildcards

ls *.txt          # every file ending in .txt
cp *.jpg photos/  # copy all the jpegs at once
rm report-*       # everything starting with report-

Check before you delete: run it with ls first, and see exactly what the star matched.

* stands for "anything".

A sandbox to break

Play around

One step further

The output of one command
can become the input of the next.

Pipes and files

ls | wc -l            # how many things are in here?
ls -l | head          # just the top of a long listing
ls > filelist.txt     # send the output into a file

Pipelines can be read from right to left

ls | wc -l — count the lines, of the listing

Pipelines

Getting unstuck

Closing the window always works too.

Cheatsheet

These are some of the most common but there are a lot more.

This week

• Open the terminal once a day, for anything
• Use cd and ls instead of a double-click
• Press Tab constantly
• When something annoys you twice, ask whether you can do it with one line

Keep practicing

Resources

And the one already on your machine: man.

Questions?

$ open

presentations.hackenshaw.com/command-line/

These slides, with cheatsheet and link to notes.txt.

$ thanks for coming

cmdbox

$ open cmdbox.hackenshaw.com