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What is Commit

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  • git obj types 중 하나이다.
  • 목적? snap shot

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  • Commit includes Author name and email, description (and parent), and pointer.
  • Commit is just "wrapper" for the tree obj and contains pointer to specific tree
  • By moving to different commits(checking out) you are able to "travel" between different "versions" of the project

Configure Git author name and email

# Set git author name and email
git config --global user.name "dev090613"
git config --global user.email "128305501+dev090613@users.noreply.github.com"

git config --list

# user.name=dev090613
# user.email=128305501+dev090613@users.noreply.github.com
  • It's recommended to set in your local git config name and email same as used at GitHub account.

Creating first commit

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  • They are in staging area(index)
git status
# Changes to be committed:
# ...

git ls-files -s
# 100644 b7aec520dec0a7516c18eb4c68b64ae1eb9b5a5e 0	file1.txt
# 100644 4400aae52a27341314f423095846b1f215a7cf08 0	file2.txt

git commit -m "Our very first commit in the project"
# [main (root-commit) 36e4080] Our very first commit in the project

# 새로운 SHA1 hash( 36e4080 )가 생성되어 .git/objects/ 에 저장되었다. 이 hash-obj는 commit이며 tree의 포인터를 포함한 여러가지 정보를 담는다.
# working directory에 저장된 files를 기반으로 git repo에 새로운 obj를 저장한 셈

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Exploring commit object

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# To check contents of commit obj
git cat-file -p 36e4080


tree 3b95df0ac6365c72e9b0ff6c449645c87e6e1159 # Pointer of tree obj
author dev090613 <128305501+dev090613@users.noreply.github.com> 1690285932 +0900 # Author name and email
committer dev090613 <128305501+dev090613@users.noreply.github.com> 1690285932 +0900 # Committer

Our very first commit in the project # Description

Current project state overview

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# 세 가지 커맨드 비교

ls -l # Working directory
git ls-files -s # Staging area(index)
find .git/objects/ -type f # git repo

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Basic Git commands

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git status # current state of git repo
git add # Add files from working directory to staging area
git commit # Creates new commit obj in git repo. and it also creates new blobs and trees
git log # History of changes(commits)
git checkout # Checkout commit or branch. you can travel between different versions of your project.

Adding new file to working directory

git log

commit 36e40801f4371df86146bb5b12de8da4e5d040ce (HEAD -> main)
Author: dev090613 <128305501+dev090613@users.noreply.github.com>
Date:   Tue Jul 25 20:52:12 2023 +0900

    Our very first commit in the project

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echo -e "This is third file in our Git repository" > file3.txt

# file3.txt is absent now in the staging area
git ls-files -s
# 100644 b7aec520dec0a7516c18eb4c68b64ae1eb9b5a5e 0	file1.txt
# 100644 4400aae52a27341314f423095846b1f215a7cf08 0	file2.txt

git status 
# Untracked files: 
# 		... file3.txt

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  • File tracking status in Git
    • Untracked/ Modified/ Staged/ Unmodified

Git files lifecycle

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  • To Tracking file(Stage), Type git add <file_name>

Stage file

# 방법 1: 전부 staging
git add . # dot is argument

# 방법 2: 특정 File staging
git add file3.txt
git ls-files -s

100644 b7aec520dec0a7516c18eb4c68b64ae1eb9b5a5e 0	file1.txt
100644 4400aae52a27341314f423095846b1f215a7cf08 0	file2.txt
100644 289960fd4f172ef29a9bf30f9c49c1725ca253dc 0	file3.txt

# file3.txt 가 staging area에 추가됐음을 확인할 수 있다.

Unstage file using git rm

git status

Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
	new file:   file3.txt	
# file3.txt가 staging area에 위치하고 있음

# To unstage specific file
git rm --cached file3.txt # output: rm 'file3.txt'

git ls-files -s
# 100644 b7aec520dec0a7516c18eb4c68b64ae1eb9b5a5e 0	file1.txt
# 100644 4400aae52a27341314f423095846b1f215a7cf08 0	file2.txt

git status
# Untracked files: file3.txt

git add file3.txt

Commit changes

  • git commit : files을 staged state에서 unmodified state로 옮긴다.
    • It will create new commit obj, create new blob obj for file3.txt and create new tree obj
git commit -m "Second commit"


[main a09ece8] Second commit
 1 file changed, 1 insertion(+)
 create mode 100644 file3.txt
 
# 이로 인해 file3.txt에 대한 hash-object가 git repo에 생성되었을 것이다. (working directory의 file을 기반으로 git repo에 obj를 생성한 것)
# file1.txt와 file2.txt에 관한 것은 이전에 이미 생성되었다. low-level로 직접 작성. (git repo에 직접 생성하였었고, git read-tree, checkout-index 하여 working directory에 가져왔었음 )

Exploring changes in Git repository

git status # nothing to commit, working tree clean

git log
# Part of hash in second commit: a09ec


git cat-file -p a09ec

tree 31b1e96ca47eb9a6c2a506d8a1d6530da7786ea7
parent 36e40801f4371df86146bb5b12de8da4e5d040ce # Pointer to parent commit
author dev090613 <128305501+dev090613@users.noreply.github.com> 1690297384 +0900
committer dev090613 <128305501+dev090613@users.noreply.github.com> 1690297384 +0900

Second commit
# parent commit 을 확인해보자. 이는 root commit이다.
git cat-file -p 36e40


tree 3b95df0ac6365c72e9b0ff6c449645c87e6e1159
author dev090613 <128305501+dev090613@users.noreply.github.com> 1690285932 +0900
committer dev090613 <128305501+dev090613@users.noreply.github.com> 1690285932 +0900

Our very first commit in the project
# 두 번째 커밋의 tree를 확인
git cat-file -p 31b1e

100644 blob b7aec520dec0a7516c18eb4c68b64ae1eb9b5a5e	file1.txt
100644 blob 4400aae52a27341314f423095846b1f215a7cf08	file2.txt
# git commit을 하여 working directory에 존재하던 file3.txt에 대한 obj가 git repo에 생성되었다.
100644 blob 289960fd4f172ef29a9bf30f9c49c1725ca253dc	file3.txt

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Current diagram of Git repository

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  • 현재 repo에 7개의 Obj 존재
  • 두 Tree는 각각 폴더의 상태를 contents로 삼는 것 같다(후자는 세 blobs에 대한 Links를 가지고 있음). 따라서 두 Tree의 hash는 다르다.(fil3.txt의 존재 유무 차이가 있음)
  • second commit으로 세 개의 새로운 obj 생성.