020-first-commits.md

Alice: first commits

Now that Alice has a proper git repository in place, she can take advantage of it to start developing her novel.

Lab

• Our author wants to take a look at the current state of her repo:

git status

• Time to add the current version of the chapter to the git index (aka staging zone):

git add chapter-01.md

• The output of the add command was not very verbose, so Alice looks again at the state of the repo

git status

• Now that everything seems on its place, she will put the current text of the chapter in the repository by creating her first commit:

git commit -m "Initial draft of the first chapter"

• She wants to check that everything is being tracked as expected. To do it, she starts by using the log command:

git log

• How does the repo knows what is the current position in the chain of revisions? We can explore the structure created on disk by the commit:

cat .git/HEAD
cat .git/refs/heads/main     # Whole sha-1 HEAD

Actually, there are several ways to get the value stored in a reference. What would be the best way to programmatically retrieve the SHA-1 of the current revision?

git rev-p████ HEAD

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Solution

git rev-parse HEAD

---

• Now Alice can safely apply the new paragraph to the text, without any fear to lose the content of the previous version:

git status

ed chapter-01.md << EOF
2i

Tim is a lean and athletic young man with short brown hair and piercing blue eyes. He has a strong jawline and a sun-kissed complexion from spending so much time at the beach. His body is toned and muscular from his active lifestyle, and he exudes a sense of energy and enthusiasm for life.
.
w
q
EOF

• Good. Let's see what are the unstaged changes

git status

• The author is interested to check what are the differences (the changesets) between the current working area and the commited revision.

git diff chapter-01.md

• Looks good, so Alice puts the new changes in the git database

git add chapter-01.md
git commit -m "Added description of Tim"
git status

• Alice is happy to be able to travel through the history of all the applied changes by using the log command:

git log

• After taking a break and having her breakfast, our writer wants to refresh how was the first version of the story. She starts by listing all the available revisions:

git rev-list --all

• Alice knows how to get the SHA-1 the current revision:

git rev-parse HEAD

• And also, the SHA-1 of the previous revision, corresponding in this case to the original commit

git rev-parse HEAD~

• Being a developer, Alice cannot resist the temptation of playing with the revision SHA-1s to retrieve a particular version of the file:

PREV_REVISION=$(git rev-parse HEAD~)
echo The previous revision was $PREV_REVISION
git show $PREV_REVISION:chapter-01.md

• Although, in the end, she knows it is easier to just use the symbolic reference name:

git show HEAD~:chapter-01.md

Umh... ok... and how can Alice see the differences between the current version of the chapter and the originally commited one (two revisions ago)?

git d███ HEAD~ chapter-01.md

---

Solution

git diff HEAD~ chapter-01.md

---

Questions

• What does it mean that a set of files are untracked?
• Which command would allow you to access the version of chapter-01.md stored two revisions ago? And five?

Diagram