title: Understanding Git — Basics theme: black css: style.css revealOptions: transition: 'none'
Achilleas Koutsou
2019-07-23
Note: Who here:
Note: We'll start by looking at the basic components of a git repository and go through the basic workflow, explaining how it relates to and affects these objects
A series of snapshots with some metadata about the snapshots and their content
Note: At the highest level, a git repository is a series of snapshots with some metadata about the snapshots and their content
Note: The three basics objects of a git repository
Note: During the workflow, files cycle through a number of states, starting from untracked (unknown to git). Once added to a git repository, a file can exist in one of three states, unmodified, modified, and staged.
.------------. .------------. .------------. .------------.
| Untracked | | Unmodified | | Modified | | Staged |
·------------· ·------------· ·------------· ·------------·
| | | |
|--------------------ADD----------------------->|
| | | |
| |----EDIT------>| |
|<----REMOVE----| |----STAGE----->|
| |
|<----------COMMIT--------------|
(Adapted from https://git-scm.com/book/en/v2/Git-Basics-Recording-Changes-to-the-Repository)
Note: This illustrates the states of a file and the actions that make it transition from one to another
Note:
The state transitions shown on the previous slide, on that state diagram, correspond to git commands.
We'll go through each and explain what it does exactly before we see them in action.
Create an empty git repository in the current directory.
$ git init
Initialized empty Git repository in <dir>
$ git status
On branch master
No commits yet
nothing to commit (create/copy files and use "git add" to track)
Note: This will initialise the current working directory to become an empty git directory. It doesn't matter if there are files in the directory or not. It simply marks the directory as a git repository and ignores any files that may already be present.
The git status command shows you the current status of the repository. We'll be using it after every step to inspect the repository and check our changes.
Any files in the directory are Untracked.
$ git status
On branch master
No commits yet
Untracked files:
(use "git add <file>..." to include in what will be committed)
notes.txt
nothing added to commit but untracked files present (use "git add" to track)
Add a file in the directory to git
$ git add notes.txt
$ git status
On branch master
No commits yet
Changes to be committed:
(use "git rm --cached <file>..." to unstage)
new file: notes.txt
notes.txt is now in the Staged state.
Note that the file is prefixed with new file: under the Changes to be committed: heading.
Note: Tells git to start tracking the file.
There are still no commits, but the file has been added, which puts it in the Staged state.
Create a commit with the staged changes
$ git commit -m "First commit: Add notes.txt"
[master (root-commit) 3c1915a] First commit: Add notes.txt
1 file changed, 0 insertions(+), 0 deletions(-)
create mode 100644 notes.txt
$ git status
On branch master
nothing to commit, working tree clean
-m to specify the commit message. It should be short and descriptive.notes.txt file is now in the Unmodified state.Note:
Tracked Unmodified files don't appear in the git status output.
$ echo "Repository notes and instructions" >> notes.txt
$ git status
On branch master
Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git restore <file>..." to discard changes in working directory)
modified: notes.txt
no changes added to commit (use "git add" and/or "git commit -a")
The file is Staged to be committed.
Note that the file is prefixed with modified: under the Changes not stated for commit: heading.
$ git diff
diff --git a/notes.txt b/notes.txt
index e69de29..b0037c9 100644
--- a/notes.txt
+++ b/notes.txt
@@ -0,0 +1 @@
+Repository notes and usage instructions
Shows the differences between the working tree (the current state) and the git state.
Note:
git diff can be used to show the differences between two states of the same file (or files). Without arguments, it shows the differences between the current and last committed state. In other words, it shows the unstaged modifications made to a file since the last commit.
$ git add notes.txt
$ git status
On branch master
Changes to be committed:
(use "git restore --staged <file>..." to unstage)
modified: notes.txt
The file is Staged to be committed.
Note that the file is prefixed with modified: under the Changes to be committed: heading.
$ git commit -m "Add heading for notes"
[master b29f432] Add heading for notes
1 file changed, 1 insertion(+)
$ git status
On branch master
nothing to commit, working tree clean
We are back in the (clean) Unmodified state.
$ git rm notes.txt
rm 'notes.txt'
$ git status
On branch master
Changes to be committed:
(use "git restore --staged <file>..." to unstage)
deleted: notes.txt
$ git commit -m "Remove notes file"
[master 78e8ffc] Remove notes file
1 file changed, 1 deletion(-)
delete mode 100644 notes.txt
Note: Contrary to what the diagram shows, removal also requires a commit. It's not a direct transition from Unmodified.
$ git log
commit 78e8ffcaac604400951ee7d0340be74fb0f58bcf
Author: Achilleas Koutsou <achilleas@example.org>
Date: Thu Jun 4 21:22:36 2020 +0200
Remove notes file
commit b29f432d3d7cff92bc5e61e6bd3b04df23b673d9
Author: Achilleas Koutsou <achilleas@example.org>
Date: Thu Jun 4 21:10:06 2020 +0200
Add heading for notes
commit 3c1915a5148ac3917be1cfe78a830a383d2d7ad6
Author: Achilleas Koutsou <achilleas@example.org>
Date: Thu Jun 4 20:22:35 2020 +0200
First commit: Add notes.txt
The history of states is always available
Note: This is why clean, short commit messages are important.
$ git log --oneline
78e8ffc Remove notes file
b29f432 Add heading for notes
3c1915a First commit: Add notes.txt
The log can be formatted and condensed in many ways to make it easier to read.
Slides and accompanying material at
https://github.com/achilleas-k/understanding-git https://gin.g-node.org/achilleas/understanding-git