Git - Commit

A commit ¹⁾ in git is an object ²⁾ that stores the information about:

• who saved the file system snapshots,
• when they were saved,
• why they were saved.
• the commiter
• the author
• the parent commit

It's added in commit log (or log) behind its parent commit.

For each commit, a new snapshots (tree) of the project directory is preserved.

Commit identifier are the hash object calculated on the following inputs:

• the SHA of the all files and directories
• the SHA of all ascendant commit
• the commit message
• the author name/email/timestamp
• the committer name/email/timestamp

To reference a commit by name and not by SHA, named called ref can be used.

The commot message is given with the -m option.

git commit -m "My Commit"

List:

• GIT_AUTHOR_DATE
• GIT_COMMITTER_DATE

# Give a date to the commit
git commit --date='Wed Feb 16 14:00 2037 +0100'
git commit --date='2005-04-07T22:13:13' # Iso

# Change the date of a previous commit
# The -C HEAD is just to bypass editing the commit message
git commit --amend --date='Wed Feb 16 14:00 2037 +0100' -C HEAD

See How can I tweak the date of a commit in the repo?

git cat-file -p fdf4fc3
# where fdf4fc3 is the first characters of the commit hash

tree d8329fc1cc938780ffdd9f94e0d364e0ea74f579
parent xxxx
author Foo <[email protected]> 1243040974 -0700
committer Bar <[email protected]> 1243040974 -0700

First commit

where:

• you can see the tree
• the parent commits if any
• the author
• the committer
• and the message

The commit tree is the tree of the commit. It's an image of the file system (ie file and directory)

Get the hash of the commit tree

• short hand notation that can be used in any commdn

commitHash^{tree}
# dos: commitHash^^{tree}

For example:

• to print the hash:

git rev-parse commitHash^{tree}

• the list the tree

git ls-tree commitHash^{tree}

• With the show command

git show --pretty="" --name-only commitHash

• With the listing of the commit tree

git ls-tree $(git rev-parse commitHash^{tree})

• Get the hash

git rev-parse commitHash:path/to/file

• Get the content

git show commitHash:path/to/file

gitk the commit viewer

gitk file
gitk --follow file # for rename

git commit

echo 'First commit Message' | git commit-tree d8329f
# d8329f is the tree hash

To visualize the type of commit, you can use emoji. See a list of emoji by commit type at Emojis Commit

Git - Log (Commit History)

git log --format=fuller
git log --pretty=oneline

Undo the last commit without deleting the changed files - Reset

# --soft is the default
git reset --soft HEAD~

If you accidentally commit on master, it's not hard to fix things up. Assuming you've just made an errant commit on master:

• “Backs up” your commit, creating a topic branch

git branch myNewTopicBranch
 

• Reset your master branch to the same state as upstream/master

git reset --hard upstream/master

If you want to your working directory back to the status of upstream, see working directory purge

• commits that branch-X has but master doesn't

git log master..branch-X

Options:

• –oneline
• –stat will show the files

Git - difftool

git difftool -y origin/master..origin/develop

git checkout commit_hash
git checkout 56a4e5c08

You are then in a detached head state.

or

git checkout -b branchName commitHash

• commit