This section will be a bit of a grab bag of various tips and tricks to make your life easier. I also need to teach this because I use them so frequently I don't even think about it!

Tilda

One quick tip here is the ~, called a tilda. On USA layouts of keyboards, it's on the same key as the backtick and to the left of the 1 key. The tilda in bash represents your user's home directory. If you type cd ~ you'll go to your home directory. If you type ls ~/snap you'll list the the contents of /home/ubuntu/snap.

Slash

Similar to the above, if you say cd /, the / means root. So you'd be at the most root directory of your entire project. It's the beginning of an absolute path, so if you said cd /usr you'd end up at the usr directory in the root directory.

Up and Down

You will use this constantly. If you hit the up arrow, you'll populate the command line with the last command you ran. If you hit up again, you'll go to the one before that, and so on and so forth. If you hit down, you'll go back to a more recent command. This is super useful and I do it all the time.

Tab Completion

Most shells have a relatively robust tab completion system. When I say "tab completion" I mean you start typing something and hit the tab key, the shell will do its best to figure out what you're trying type. An example would be if I'm in a directory with two files, index.html and package.json, and I start typing cat i and hit tab, it will know the only file starting with i is index.html and will autocomplete your line to cat index.html. Saves you a lot of typing.

For another example, imagine you have two files in a folder, index.html and index.js. If you start typing cat and hit tab, it'll complete out to cat index. because that's as far it can get without assuming which file you want to open. If you hit tab again, it should show you your two options. If you then hit j and hit tab it'll complete out cat index.js for you.

Some commands are smart enough to know what sort of thing you're looking for. If you have two files, saved.txt and something-else.txt, and a folder called src, if you type cd s and hit tab, you'll autocomplete cd src because the shell knows you're looking for a folder when you're using cd.

Tab completion will always work with the file system. Some commands have tab completion too. Type git de and hit tab and it should complete to git describe for example. Admittedly I use this far less because I can never remember which commands have tab completion and which don't. The individual programs have to supply that to the shell for it to work.

Reverse Search

Instead of having to hit up a bunch of times to find a command you ran forever ago (it keeps track of something like the past 10K commands you've run), you can CTRL+R to do a reverse search (reverse meaning starting with the most recent and working background to most recent.)

Let's say I ran the command echo "hello my friends" last week and I wanted to find that command again and I only remember that it had something to do with "friends". I'd type CTRL+R and start typing "friends". If it was the most recent command that I had run with "friends" in it, it'd show up and I could hit enter and it'd run. If there was another command between now and again, I can hit CTRL+R again to look further back in the history. This is also super useful and something I do a lot.

.bash_history

The previous two things are made possible by a file called .bash_history. This file is constantly being appended to when you run commands. You don't really need to ever really edit this file but I wanted you to be aware of where it was and what it does. It's always in your home (~) directory. If you're using another shell, it'll be called something else like .zsh_history.

If you type tail ~/.bash_history you should see what the last few commands you've ran in your previous session of bash. It will only write to .bash_history once you've exited bash, it'll dump the whole session's commands into it.

One reason I want you to be aware of it is that if you say something like command --password=my_super_secret_password that will live in your .bash_history file unless you delete it. That means if someone gets ahold of your computer, they could potentially nab passwords that way. Just something to keep in mind. You can also edit the .bash_history after you run a command like that to delete it and it'll be gone.

!!

If you type !! in bash, it will replace the !! with whatever the last command you ran. So if you just type !! and enter, it'll run the last command you ran. If you run sudo !! it'll re-run the same command again but with sudo in front (we'll talk about sudo soon.)

"!" is often pronounced "bang" when it comes to the command line. When I looked at why, I found this on Wikipedia

In the 1950s, secretarial dictation and typesetting manuals in America referred to the mark as "bang", perhaps from comic books where the ! appeared in dialogue balloons to represent a gun being fired, although the nickname probably emerged from letterpress printing.

So, given that, you'll hear this frequently called "bang bang".

clear

If your screen is too full, just type clear and enter and it'll put you back at the top. You can still scroll back to see old output. CTRL+L will work too, but to be honest I can never remember it so I just use clear.

Copy and paste on the CLI

Let's talk a moment about copy and paste with regards to the command line.

1. If you're on Windows, it's a bit of a trick. CTRL+C and CTRL+V already mean something different to bash (they're signals, we'll talk about those shortly) so those don't work as you'd anticipate. You'll need to use Shift+CTRL+C and Shift+CTRL+V. Because macOS uses CMD+C and CMD+V for copy and paste and those don't mean anything to bash, nothing changes for them.
2. Be careful of what you copy and paste. If you copy something off a website, using JavaScript they can switch what you highlight with something more nefarious so that when you paste it, it doesn't do what you copied. So I could have copied echo "this is harmless" but it actually pastes send_attacker_my_passwords. Be careful that you trust where you're copying and pasting from (StackOverflow is fine!)
3. Along with the former point, the attacker can actually even include the return character to execute the command before you can even see what it is. Most emulators (like Windows Terminal and iTerm2) will warn you "hey, we found a return character in this paste, are you sure you meant to do this?" but you shouldn't rely on the emulator to save you.
4. In general it's just helpful to understand what you're doing. If you copy and paste something, make an effort to grasp what it's doing and how.