A Very Brief Shell and Git Reference

For non-technical Mac users who want to dip their toes in being technical.

1. Basic shell usage

Step 1: open a terminal

⌘+<space> -> terminal -> Enter

A window should pop up. You can type things in it. It is your computer, but presented in a text interface. This is where you will use git. Actually, you can use git from a UI, but I really really think you will be happier if you do it this way. It is not that hard.

If you think it is ugly or annoying, there are a million ways to fix that – but, later.

A few commands:

pwd : “print working directory” – tells you what folder you’re in. It will probably say something like /Users/ajk. /Users/<your login id> is called your ‘home directory’, and you can refer to it with ~. All folder locations start with / which is the ‘bottom’ of your computer.

echo <something>: echoes <something> back to you.

  • echo ~ : prints /Users/<your name
  • echo $PWD : prints the value of the variable $PWD, which is the exact same thing that pwd does.

ls : lists the current directory’s contents. Or ls <somewhere> to list the contents of something else. Maybe try:

  • ls
  • ls ~
  • ls /
  • ls ~/Desktop

In general, commands can have flags, which are parameters added with hyphens - afterwards, and arguments, which are free-standing things (without hyphens). For example, ls -alh ~ says “list the contents of ~, with the modifications -alh”. I could also write that as ls -a -l -h ~ ; you’re (usually) allowed to combine flags into one. -a means “include hidden files”, which are files whose names start with .. (Try ls -a ~ to see how many hidden files there are! The Mac UI hides them also.). -l means “list in ‘long’ format”, which has more information – specifically, filesizes. -h says “make the file sizes human-readable, using prefixes like G for gigabyte instead of just a huge number.

(note: every command has different flags. Most (though not ls) have -h for ‘help’ and -v for ‘verbose’, though.)

cd <directory> : change directory: moves directories. Your options are:

  • relative folders, like cd Desktop.
  • absolute folders, like cd /Users/<your id>/Desktop
  • . : the current folder, always. (cd . does nothing).
  • ..: the parent folder, always. So cd .. when you’re in /Users/<your id> takes you to /Users.

A couple other useful things:

which <command> : tells you where a command is located. For instance, when I type which git I get /usr/bin/git. If I type ls /usr/bin I will see a list that includes git.

less <file> : opens a file to read as text. The UI is very unintuitive. b goes down and d goes up and q quits. Actually, less is fantastic, but it’ll be a while before you’re used to it. There are tons more features. Just don’t ask about the name (okay – it’s a pun on its predecessor more which showed you ‘more’ of a file).

man <command> : opens the ‘manual’ for the command. It’s usually a huge pain to read cause it’s wordy, but it does usually have what you want. It’s normal to not tell you, really, how to use a tool – once you know it exists you can look it up in man. It opens the manual in less so don’t forget about b, d, and q.

cat <file> : catenates the contents of the file to the terminal. Good for quickly reading short things.

rm <file> : removes a file. rm -r to remove directories and all their contents. Be very careful…

open <something> : opens the target in the explorer, if you’re tired of typing and would rather start clicking.

mv <file> <destination> : moves something to a new location. Also used to rename things.

cp <file> <destination>: copies a file.

mkdir <name> : makes a directory.

If a command ever does things and won’t stop, type ctrl+C or ctrl+D. They work slightly differently, but usually one will stop whatever’s going on. In shell-lingo ctrl is written as ^C, so these are ^C and ^D.

Now try:

yes : just says ‘y’ repeatedly. Weird, right? You’ll need ^C to get it to stop.

2. Getting Git

I am not sure if you will already have Git set up on your computer. If not, the best, though not easiest, way to do it is going to be:

  1. Install HomeBrew, which is a ‘package manager’ for Macs, and will let you install tons of stuff with a single line in the terminal. See here for instructions.

  2. Install Git with Homebrew, by typing brew install git. Thereafter git should exist in your terminal.

Why use Homebrew? Because you can also type brew install r or brew install python (though you might have that already) or a million other things.

There is some setup that will be necessary later also:

  1. Set up your user name, via git config --global user.name "<your name>".
  2. Set your email, via git config --global user.email "<email@example.com>". Your commits will be tagged with these two.
  3. Make a Github account here.

Now, I’m not sure what you want to do with Git or what repositories you’re interested in touching, so I’ll leave the rest of Github discussion for you to figure out. But first, a primer on Git.

3. Git Basics

Git is a way of saving and sharing your work. You could just … save it and email it, I guess. But Git is more robust. It lets you do things like:

  • look at how a file changed over time
  • merge two changed versions of a file into one new version
  • revert a change to a file to an old version because it broke something
  • take someone else’s work and fork it into a new version that you modify.
  • switch between multiple versions of your work that coexist on your computer in the same place, called branches.

Git creates things called repositories (colloquially ‘repos’) and links them together. A repository is a folder on a computer that has a .git hidden directory, which is filled with secret git-related information.