Git - Commit

About

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.

Property

Identifier

SHA

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

Name

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

Message

The commot message is given with the -m option.

git commit -m "My Commit"

Author and Committer Date

• The date of a commit is the author date.
• There is also a committer date.

Committer / Author

A commit has a:

• Commiter
• and a Author

See

Cat file

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

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

Last commit

Just for the last commit

git cat-file -p HEAD

Tree

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}

List the files in a commit

• 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})

File in a commit

• Get the hash

git rev-parse commitHash:path/to/file

• Get the content

git show commitHash:path/to/file

Commit viewer : gitk

gitk the commit viewer

gitk file
gitk --follow file # for rename

Management

Creation

git commit

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

Visualization

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

List

What is the Git Log (also known as commit history or commit log) ?

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

Undo

Soft

Undo the last commit without deleting the changed files - Reset

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

Hard

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

Modify

the Last Commit

git commit --amend args

Example:

• last message

git commit --amend -m "another commit message"

• the author's date

git commit --amend --date='Wed Feb 16 14:00 2037 +0100' -C HEAD

Delete the last local commit

• The last commit if not pushed

git reset HEAD~

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

Diff

Command line

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

git log master..branch-X

Options:

• –oneline
• –stat will show the files

DiffTool

Difftool

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

Checkout

git checkout commit_hash
git checkout 56a4e5c08

You are then in a detached head state.

or

git checkout -b branchName commitHash

Get the number of commit since a period

PERIOD_HOURS=4
git log --oneline --since '$PERIOD_HOURS hour ago' | wc -l

Documentation / Reference

• docs/git-commit.html