Day 4
The time machine that is Git
These commits are incremental and ultimately building something. As time passes, you will have something to teleport back to (and once you have gotten that sample-that elusive nugget of data-and then go back to the present).
Commands in Play
git log --parents
git log --parents --abbrev-commit
git log --oneline
git log —-patch
git log —-stat
git log —-patch-with-stat
git help commit # then `/DISCUSSION` to skip ahead to the value of extended commit messages
git rev-parse HEAD # `git rev-parse` translates branch names to their corresponding SHA1 IDs
git rev-parse main
git checkout _short-SHA1-fragment_ # Go back to that version, results in "detached" HEAD!
Note: checking out ‘$short-SHA1-fragment’.
You are in ‘detached HEAD’ state. You can look around, make experimental changes and commit them, and you can discard any commits you make in this state without impacting any branches by performing another checkout.
If you want to create a new branch to retain commits you create, you may do so (now or later) by using -b with the checkout command again. Example:
git checkout -b new_branch_name
git commit -m "head of message" -m "this is another line" -m "still got more to say"
git rev-parse main~3
git show main@{3}
git show main^^^
git rev-parse :/"$some-commit-string"
git log --parents --abbrev-commit.
Test Your Knowledge
Q. How can you list the history from the first commit to the last?
Q. Is there a way to list just the most recent N commits? (Where N can be any number?) How?
A: Use -<n> to show only the last n commits.
Q. Can you display the date as time relative to the current time (for example, 2 hours ago)?
A: Git log can take the time-limiting options such as —since and —until . E.g. git log —since=2.weeks
Q. I’m a big fan of git —oneline, but it’s a shortcut. What is it a shortcut for?
A: It is like git —pretty=oneline --abbrev-commit used together. Refer to git-scm doc.
8.5.3 Test Your Knowledge → Using other names
Q. What commits do each of these commands point to?
| Git Command | Returns |
|---|---|
git rev-parse HEAD | b34cc05c5e558a9ab0df939ec51ee607a80bb53f |
git rev-parse main | b34cc05c5e558a9ab0df939ec51ee607a80bb53f |
A1: git rev-parse HEAD points to the SHA1 ID of main.
| Git Command | Return |
|---|---|
git rev-parse main~3 | fbae4301505809053a5eb2659a5fc2f8cb5c8e61 |
git show main@{3} | commit fbae4301505809053a5eb2659a5fc2f8cb5c8e61 \n Author… |
git show main^^^ | commit fbae4301505809053a5eb2659a5fc2f8cb5c8e61 \n Author… |
A2: git rev-parse main~3 points to the third historical commit below HEAD -> main. git show main@{3} returns the metadata from the commit and a diff --get. git show main^^^ does the exact same as the former command.
Q. What did the last git rev-parse search to find its commit?
| Git Command | Return |
|---|---|
git rev-parse :/"subtract" | fbae43d15d58b9053a5eb2659a5fc2f8cb5c8e61 |
A: It searched commit messages and returned the SHA1 ID.
Q. Does git rev-parse work on tag names?
A: git rev-parse $your-tagname did not appear to work.
Q. Do these symbols (~3, @{3}, and so forth) work on tag names?
A: git show $your-tagname^ took me to the SHA1 ID for that tag.
More Resources
SHA1 IDs and computing collisions
Subtlety of origin\HEAD in a clone