2021-01-05
It's taken longer than I initially planned to come to the point where I'm ready to initiate you into the secret arts of git wizardry, but I think we're now ready. We've learned how to speak computer and use the terminal instead of just clicking your cursor, and how to write and execute programs, even when it requires compiling your code.
So, git ready for a series of terrible puns where I pretend that the
'e' in get and the 'i' in git are indistinguishable.
To begin with, let's install the program:
sudo apt install git
Or if you're not using Debian, you should be able to find some installation instructions here.
Check you've installed it successfully and can run it from the command-line, just by checking the version:
git --help
And you should see a list of the common Git commands. Let's use a few of them.
Say we had a folder with our hello_world scripts:
mkdir hello_world
cd hello_world
echo 'echo "Hello World"' > hello_world.sh
echo 'print("Hello World")' > hello_world.py
Then we can initialize Git version control just like this: git init.
And you should get a message telling you that you have "Initialized empty Git repository".
Now you ask for the git status, and you will be told that you have
'No commits yet', but there are 'Untracked files'. So let's add them!
Just one at a time, so we can see what happens.
Let's start with the Bash script: git add hello_world.sh. Now if you
check the git status, you will be told there is a "new file" with
"changes to be committed". But those changes aren't 'committed' yet,
because git add just 'adds' it to the 'stage'. Which means if you git
reset hello_world.sh then you'll go back to having two untracked files
and no commits. But if you git add the file to the staging area and
then git commit -m "Add Hello World Bash script", then when you ask
for your git status it will no longer complain that you have "No
commits yet". Which means you can look at the git log and see the
record of your Bash script being added to the repository.
Now do the same for the other file: git add hello_world.py; git
commit -m "Add Hello World Python script".
And you've got both files committed to version control. Which means now
we can do something crazy: we can edit our code, without fear of
breaking things irreparably. First let's checkout a new branch: git
checkout -b my-new-branch. And then let's overwrite our Python script
with a more expansive greeting: echo 'print("Hello Universe")' >
hello_world.py. You run it, python hello_world.py, and if you haven't
got those double and single quotes tangled up, then you might get the
desired cosmic greeting. So now you git add hello_world.py to the
branch's stage, git commit -m "Make greeting more inclusive", and then
you can git checkout master.
Pause to see that the master branch currently has the old greeting. If
you git checkout my-new-branch you can find it again. But now git
checkout master, and then merge the changes from your branch:
git merge my-new-branch.
And now you're using version control like a professional software engineer. Next time I'll talk about GitHub, and things will get even more exciting.