Useful commands

computers have so many commands! it is hard to remember them all. hopefully this page can help for the next time you are staring nervously at the shell.

by category

navigation

command	example	description
cd	cd ../folder/subfolder	change directory from one folder to another
ls	ls	list the contents of a folder
pwd	pwd	print the full working directory you're currently in

media

command	example	description
magick	magick in.png out.jpg	convert image files
ffmpeg	ffmpeg -i in.mov out.mp4	convert video and audio files
yt-dlp	yt-dlp https://youtu.be/INa_SYywZis	download videos & audio from YouTube and other platforms

text

command	example	description
cat	cat in.txt	print out a file
less	less in.txt	page through a file
head	head -n 5 in.txt	view the beginning of a file
tail	tail -n 5 in.txt	view the end of a file
grep	grep "search" in.txt	search a file for some text
sed	sed -i 's/old/new/' in.txt	find and replace text in a file
nano	nano out.txt	a pretty simple text editor, like the "Notepad" of linux
emacs	emacs out.txt	a really powerful text editor that's a bit harder to use
vim	vim out.txt	an unhinged text editor that some people have opinions about

web

command	example	description
wget	wget http://a.horse/disc.iso	download a file
curl	curl http://ip.me	send a HTTP request to a server
caddy	caddy run	host a web server
php8.4	php8.4 page.php	run a php script and check it for errors

network

command	example	description
dig	dig pronounmail.com	lookup DNS records for a domain
nslookup	nslookup pronounmail.com	lookup DNS name server for a domain
ping	ping pronounmail.com	check if two computers can see each other
lsof	lsof -i -P -n	list open ports on the current machine

services

command	example	description
systemctl	systemctl status my_unit	start/stop/check statuses of services
journalctl	journalctl -xeu my_unit	check logs for a service

help

command	example	description
tldr	tldr git pull	command usage examples
man	man git	command usage details

funky things you can do in the shell

the shell has a lot of funky features!!

put stuff in a file

If you want to take the stuff a command is printing out and instead of printing it out, put it in a file, you can use the > symbol. For example, if you wanted to take the last line of a long file and copy it to another file you could do:

tail -n 1 long_file.txt > last_line.txt

Just one > will overwrite the file if it already exists. If you use two like this >> it will append stuff to the end of the file if it already exists.

chain commands together

There's a really powerful feature of the shell called "piping" that lets you chain multiple small commands together to do something more complex. You can use the | character for this. For example, if you have a command that prints out a lot of stuff, you can trim it to the last 50 lines and then search for the text "keyword" by chaining commands together like this:

cat long_file.txt | tail -n 50 | grep "keyword"

run multiple commands at once

You can have one command run only if another one succeeds by chaining them together with &&. If you don't care whether the first command succeeds, you can use ; instead.

You can run a command in the background by putting & after it. Just be careful cuz a command running in the background can't be stopped like normal with Ctrl+C. Instead, you'll need to find it's PID and use the kill command.

paths

Every file on a computer has a path which is how you get there. Imagine we had some folders like this and you're currently hanging out in /home/me/folderA

/
↳	home
	↳	me
		↳	folderA
			↳	file1.txt
			↳	file2.txt
		↳	folderB
			↳	file3.txt

Imagine you wanted to print out the contents of file3.txt, there's a few ways you could do this:

cat /home/me/folderB/file3.txt – use the full absolute path

cat ../folderB/file3.txt – use a path relative to .. the parent directory right above your current folder which right now, happens to be /home/me

cat ~/folderB/file3.txt – use a path relative to ~ your home directory which for the user me will always be /home/me