explaining git

source/_posts/handy-git-recipes.md

@@ -0,0 +1,88 @@
+---
+title: handy git recipes
+date: 2023-05-01 19:28:52
+tags:
+- Programming
+---
+
+[Git](https://git-scm.com/) is one of these things I use on a daily basis, yet I've never felt like I truly mastered it.
+There's so many things you can do with it, and so many ways to do them, that it's easy to get lost in the sea of commands and options.
+Truth be told, just a couple of them are enough to leverage 90% of the power of git repositories and cover the main
+needs of developers. That remaining 10% can be quite useful during complex workflows.  
+I've put together explanations of the most commonly used terminology and commands, as well as some recipes which
+I often find myself using at work. I hope you'll find them useful too. For the record, at the time of this writing
+I was using git version 2.37.0.
+
+## Terminology
+
+### Commits and Branches
+
+A **commit** is a snapshot of all the tracked files in your project. It contains the changes made since the previous commit,
+along with metadata such as the commit author, timestamp, and a message describing the changes. Commits are organized sequentially,
+each commit pointing to its parent commit. This is how git records the history of a repository. Think about it
+in terms of inheritance, instead of time: a commit inherits the changes of its parent commit, and adds its own changes
+on top of them. Everything in git is relative to something prior. More formally, commits are organized as a
+[directed acyclic graph](https://en.wikipedia.org/wiki/Directed_acyclic_graph). This way, it is easy to traverse the history
+of a repository and do all kinds of useful operations on it.
+
+![Git commits](http://localhost:4000/commits.png)
+
+Every commit is identified by a unique hash, which is a 40-character hexadecimal string. When working with commits, it's rarely necessary to
+reference them by their full identifier. You can pass in only a prefix (first 7 characters should be enough), as
+git is smart enough to figure out the rest, as long as there exists only one commit with the given prefix. For example, let's consider
+commit [dc2727cdfe357e4caf40f9c79c35d5232195ca45](https://github.com/apetenchea/cdroot/commit/dc2727cdfe357e4caf40f9c79c35d5232195ca45)
+from this blog's [repository](https://github.com/apetenchea/cdroot). You can check the metadata associated with it
+by running `git --no-replace-objects cat-file commit dc2727c`. The output is:
+
+```
+tree 2f3a693e39a75ae5e393c226c17895e6136d2d72
+parent b200f511526c750833abf07dd5749aad7be1132b
+author Alex Petenchea <alex.petenchea@gmail.com> 1682878857 +0300
+committer Alex Petenchea <alex.petenchea@gmail.com> 1682878857 +0300
+gpgsig -----BEGIN PGP SIGNATURE-----
+
+ iQIzBAABCAAdFiEE9yeY4Rbw/gqLPsLv9wg11DTo7E8FAmROsYkACgkQ9wg11DTo
+ 7E83CBAAxqwUzVdxOlMKxV5rsEs0Mx1/mh4O3dY4onjC7FZ5R/WFmNiMEGN9gDMP
+ u9V72rj0kIvr4i+TERciueR5hgEZBcpo8fO2knZPXJMe3JrOZx1cF5Fe5dGQLgi2
+ cIC8MwH3GUacRqpezFrFJWVbKtTY/mQ6a5UVOjZyg9kqJwE/otp7FgaR2Y0rC1kP
+ hGU0N4lkWnlkaUxc9K4tNYfZgahKTQGug961T5wSxFLh6qlRj27shZQ7N9JKUCIn
+ L+70hTJaLruisnqqgBse93OcCgFLOWuBkR5oxRe5vx5ZiLkXVZT9xusVpLpRxFEz
+ CvlBTQpgJ9wlWujFJdw76015UMctEjnO+M3oGC5vAfYTmYxgyDQ9suWQDdbuULpV
+ /ndA9LvZ72+BBgpIhTGOSSHcyg/Rd3A/trGgmZVkn4GAGCZJGzADKePANcPgs+iD
+ AjdehqPwwwH/82Il2shojNMJ4mPt80gWE2W0DZypvneIrbZvQ59gDnXkjhF20tCr
+ /xTRnfDVTq0pPfoeQ5Ks9f4Box+nIDdiB5FRdaddx1JDSiIWOu7dWCnfMCQDl2Ml
+ aZgD6P+8SADCo/9NWqn/vSenzxFHtmXILrTasj58ed0hOVIPNvcCBRS2d/tbs/lx
+ ozn2PNOUQvYUTfjt7SfR2Rjl3EvUFdrADdcDRb0G+Ox7yd0/JL4=
+ =Q1hH
+ -----END PGP SIGNATURE-----
+
+Minor fixes
+```
+
+That is:
+- The source tree: SHA-1 hash of the tree object representing the repository's file structure at the time of the commit.
+- Commit parent(s): The SHA-1 hash(es) of the commit parent(s). A commit can have multiple parents in the case of a merge commit.
+- Author: the name and email address of the person who authored the changes, along with the commit timestamp.
+- Committer: the name and email address of the person who made the commit, along with the commit timestamp. This might be 
+  different from the author if the changes were committed by another person.
+- GPG signature: this is optional, and can be used to verify the authenticity of the commit. It is generated using the author's
+  private key, and can be verified using their public key.
+- Commit message: the text of the commit message.
+
+All that information is combined and hashed using the SHA-1 algorithm to produce an unique commit identifier. Here's
+how you can generate it yourself:
+```bash
+(printf "commit %s\0" $(git --no-replace-objects cat-file commit dc2727c | wc -c); git cat-file commit dc2727c) | sha1sum
+```
+
+For an explanation of the command above, check out [Carl Mäsak's gist](https://gist.github.com/masak/2415865). And finally,
+to inspect the changes introduced with this commit, you can run `git show dc2727c`.  
+The usual workflow is to add changes to the staging area, and then commit them.
+```bash
+git add . # stage all changes
+git commit -m "explaining git"
+```
+
+Moving on to branches, a **branch** is just a pointer to a commit. When you create a new branch, it points to the same commit as the branch
+you created it from. When you commit changes to a branch, the branch pointer is updated to point to the new commit. 
+The default branch of a repository is usually called `master` or `main`.