https://www.youtube.com/watch?v=Qp927R-Xu1c&list=PLuHgQVnccGMA8iwZwrGyNXCGy2LAAsTXk
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There are 2 advantages on the created versions.
1. You can see "differences on each version of project" and you can see "specific past version".
2. You can go back to any state of project
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You can pass options to "git log"
# print the differences on 2 commits-based code
# using information from each commit
git log -p
# version 4
+++ b/f1.txt
# version 3
--- a/f1.txt
+f1.txt : 2
version 4 에서의 내용
-source : 2
version 3 에서의 내용
--- /dev/null
이전 version 의 내용 : 파일이 없었음
+++ b/f2.txt
위의 version 의 다음 version 의 내용
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# print all previous commits
git log hash-value-of-commit
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# print the difference on 2 codes
git diff hash-value-of-commit1 hash-value-of-commit2
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# You edit code, save code, run
git diff
then you'll see history of changes you did just ago
"git diff" is useful when you review before commit