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How I Use Git

Posted on 13 mins read Tags: Git
Table of Contents

Welcome!

This article will be a guided tour of how I use git.

We’ll talk about configuration of git itself, the aliases and scripts I’ve written, and the other tools I work with.

Since this article is quite long, here’s a table of contents:

Introduction

Talk is cheap, show me the code

Everything can be found in my dotfiles repo.

Feel free to read, but please don’t use it directly: the code was written to be used by only one person: me. Unless you are my hidden tween brother, it’s very likely to be not suited for you.

Location of the config files

I prefer having my git configuration files in ~/.config/git/config rather than in ~/.gitconfig.

That’s a matter of personal taste, of course, but it’s also conforming to the XDG directory specification

Why did you bother writing this?

Several reasons:

  • People seem to like it when I talk about theses things (as seen by the relative success of the How I Lint My Python article)
  • When describing my configuration files and work flows to others, I tend to find things that can be improved.
  • I always hope you can learn a few things from my experience (otherwise, why would I share it?)

With this out of the way, let’s dive in!

Options

Excluding files

I like to keep a separate list of file patterns I always want to ignore, without to touch the .gitignore of all the projects I contribute to:

# in ~/.config/git/config
[core]
excludesfile = ~/.config/git/excludes
# in ~/.config/git/excludes
# Vim
*.swp

# QtCreator
CMakeLists.txt.user
*.autosave

rerere

rerere stands for replay recorded merge resolution.

You have to explicitly enable it:

[rerere]
enabled = true

Let’s see it in action:

  • I’m working on a branch called new-feature, which started one week ago.
  • I decided to rebase against the latest master version:
$ git fetch origin
$ git rebase oirigin/master
First, rewinding head to replay your work on top of it...
Applying: new feature
...
CONFLICT (content): Merge conflict in bar.txt
Recorded preimage for 'bar.txt'  # <---- rerere
error: Failed to merge in the changes.
Patch failed at 0001 new feature
$ git mergetool
# fix conflicts
$ git rebase --continue
Applying: new feature
Recorded resolution for 'bar.txt'. # <--- rerere

Thus, assuming both master and new-feature continue to change and we need to re-run git rebase:

$ git rebase origin/master
 bar.txt | 1 +
 1 file changed, 1 insertion(+)
First, rewinding head to replay your work on top of it...
Applying: new feature
....
Falling back to patching base and 3-way merge...
Auto-merging bar.txt
CONFLICT (content): Merge conflict in bar.txt
Resolved 'bar.txt' using previous resolution. # <--- rerere

Note that in this case , you will get a message saying No files need merging if you try to run mergetool as usual. Instead, use git add:

$ git add bar.txt
$ git diff --staged -- bar.txt # Check that the changes still make sense
$ git rebase --continue

If you don’t like having to type git add explicitly, you can tell git to do it for you:

[rerere]
autoUpdate = true

pull

By default, pull in nothing more than git fetch followed by git merge.

I usually prefer rebases over merges, so I configured git pull to always perform a rebase:

[pull]
rebase = true

If I really need to merge, I’ll run:

$ git fetch origin
$ git merge origin/master

rebase

By default, git will show you a summary of what changed (a diffstat) in many cases, like a fast-forward merge:

$ # on master, behind origin/master
$ git merge
Updating 24878f5..5be8c2e
Fast-forward
 bar.txt | 1 +
 1 file changed, 1 insertion(+)

But it will not do that if you are not fast-forward and rebase a different branch, unless you have:

[rebase]
stat = true

The reason may be that computing the diffstat is expensive (at least more expensive than the actual merge in many cases), but personally I don’t mind the cost in time.

Usually this information allow me to be aware of the potential conflicts.

fixing history

Let’s assume you have a list of 3 commits, the last one being a fix of the first:

# edit foo.py
$ git commit -m "Foo: add bar() method"
# write some code in bar.py
$ git commit -m "Bar: add baz() method using Foo"
# realize a crash, patch foo.py again

Now, you want the third commit to be squashed with the first one. This will make code review easier and a cleaner history.

There are two ways to fix this:

First, you can make a new commit and run git rebase --interactive:

$ git commit -m "Fix Foo.bar() crash when called without arguments"
$ git rebase -i master
pick bbace84 Foo: add bar() method
pick 5499c6d Bar: add baz() method using Foo
pick 33c32e1 Fix Foo.bar() crash
# Edit file to have:
pick bbace84 Foo: add bar() method
fixup 33c32e1 Fix Foo.bar() crash
pick 5499c6d Bar: add baz() method using Foo
# quit and save
Successfully rebased and updated refs/heads/foobar.

Or (and this is quicker), make sure your last commit starts with fixup!, followed by a prefix of the message of the commit you want to fix.

Then set:

[rebase]
autosquash = true

Afterwards, when you’ll run git rebase -i, the line fixup will magically appear:

$ git comit -m 'fixup! Foo: add bar'
$ git rebase -i master
# check the "rebase-todo" file is correct
# done!

merge

[merge]
tool = kdif3

I use KDiff3 mainly because I’m too used to it to change. Some facts:

  • Cons:
    • It’s big and slow and depends on KDE4
    • It makes annoying sounds (which is the cause for the huge dependency on KDE4 …)
    • It is able to solve conflicts that git does note handle automatically, which is nice, but sometimes this goes wrong. (it’s pretty rare though)
    • It lets select you to choose ‘A’, ‘B’ or ‘C’ for the conflicts, but sometimes you want to edit the line directly in ’D’, and the the editor is painful to use.
  • Pros:
    • It shows you four windows: ‘A’, the common ancestor, ‘B’, the file from your side, ‘C’ the file from the other side, and ’D’, the result of the merge.
    • You can use “quick&dirty” resolution methods, such as “Choose ‘C’ everywhere”, or “Chosse ‘C’ for all unresolved conflicts”

Thus, when KDiff3 fails, I often just edit the un-merged file directly in Neovim and deal with the conflicts markers (<<<<<<, =======, >>>>>>) manually 1.

Note: git automatically writes a .orig file during merge resolution for backup purposes.

You can turn off this feature with:

[merge]
keepBackup = false

It took me a while to figure this out, but KDiff3 also writes a .orig file when it’s done, so you have to untick a box in KDiff3 settings window for the .orig file to really be gone.

Aliases

I have a lot of aliases. Some of them are quite common:

ci = commit
co = checkout

Since I never managed to remember how many m there are in amend, I have:

mend = commit --amend

Log

You’ll find dozen of people trying to get a colorful and useful git log.

Here’s my take on it:

lg = log --color --graph --pretty=format:'%Cgreen%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit
lgs = log --graph --pretty=format:'%Cgreen%h%Creset - %s %C(yellow)%d' --abbrev-commit

The trick is to grok the pretty format string. You’ll find all the relevant information in the git documentation.

Cherry-pick

Sometimes you want to cherry-pick a bug fix from the development branch to the release branch. In that case, adding the -x option causes the original sha1 not to be lost:

$ git cherry-pick -x develop
$  git log
Critical bug fix

(cherry picked from commit af123ed)

To make sure I don’t forget the -x, I created dedicated aliases:

ck = cherry-pick
ca = cherry-pick --abort
cx = cherry-pick -x

Rebase

When you run git rebase -i, git will prompt you to run git rebase --skip, or --continue. And sometimes you’ll want to abort. I made it so that in any case, I only have two letters to type:

ri = rebase -i
rc = rebase --continue
rs = rebase --skip
ra = rebase --abort

(Note that the alias that runs --abort ends with the letter a, like the alias for cherry-pick --abort)

Usually, I’m either at work and there’s a central repository at origin, or I’m contributing to an open source project and I have a upstream origin.

So this means I need two different aliases:

ro = rebase -i origin/master
ru = rebase -i upstream/master

go

go is reset --hard. It’s just that almost never use git reset without this option, so this is more handy:

go = reset --hard

@{u}

@{u} is a special syntax that means “the remote ref of the tracked by the current branch’. So if you are on master, this usually is origin/master

Since @{u} is hard to type, I have a few aliases, all ending with u:

gou = reset --hard @{u}
logu = log @{u}
diffu = diff @{u}

For the same reason, I often need to compare with origin/master, so this time the aliases end with o:

logo = log origin/master
diffo = diff origin/master

Helper scripts

As aliases

Git allows to insert small pieces of bash code instead of just a replacement string when you start the right value with a bang:

[alias]
prune-merged = !git branch --merged | grep dm/ | grep -v "\\*" | xargs -n1 git branch -d

At work we all prefix our dev branches with our initials, but I often forget to delete them when I’m done.

This alias looks for all the local branches that are fully merged and start with dm/ and deletes them.

Note how we use xargs -n1 to by-pass the fact that git branch -d only takes one argument.

As standalone files

By default, when you run git foo, git will look for an executable anywhere in $PATH named git-foo and run it.

(If you are wondering, the built-in commands like fetch or push are in /usr/lib/git-core/)

You can combine this with aliases to get nice names for the helper scripts you write, while still having to type fewer letters.

Lazy push

For instance, I have:

[alias]
fp = fpush

And then in I have a script named bin/git-fpush:

#!/bin/bash

set -e

function main() {
  if [[ -z "$1" ]] ; then
    echo "Missing file name"
    return 1
  fi
  if [[ ! -f "$1" ]] ; then
    echo "$1 is not a regular file"
    return 1
  fi
  git add $1
  git commit -m "Update $1"
  git push
}

main "$@"

This means that when I type git fp foo, git will expand the alias to git fpush, and then run the git-fpush script.

I use the script mostly in private repositories, when all I want is to commit just a file, without bothering with a real message.

In the same vein, I have an other script that does everything it can to push all the changes in just one command:

#!/bin/bash

set -e

function main() {
  if [[ -z "$1" ]] ; then
    echo "Missing commit message"
    return 1
  fi
  git commit --all --message "$1"
  git push
}

main "$@"
[alias]
cp = commit-and-push

Rebase

Lastly I have a helper script to rebase the last ‘n’ commits, because, as you could have guessed, I spent a lot of time rebasing stuff.

So git rebase -i HEAD~5 becomes git r 5.

Same idea, a bash script:

#!/bin/bash

set -e

function main() {
  if [[ -z "$1" ]] ; then
    echo "Usage git r <number of commits>"
    return 1
  fi
  git rebase --interactive "HEAD~$1"
}

main "$@"

and an alias:

[alias]
r = rebase-n-commits

Returning to the top directory

I use this command a lot. Here’s the implementation:

function gcd() {
  topdir=$(git rev-parse --show-toplevel)
  if [[ $? -ne 0 ]]; then
    return 1
  fi
  cd "${topdir}/${1}"
}

Assuming I’m the root of the repository is foo and I’m in foo/src, gcd will send me to foo, and gcd include to foo/include.

Note the call to git rev-parse which allows you to not try and duplicate the logic used by git to find the top level directory (hint: it’s harder than you think)

Gui tools

I do most of my git commands from a shell, but I sometimes need a graphical interface (And use a mouse)

gitk

I use gitk when I want to:

  • Have a high-level view of the history of several branches. (Use gitk --all for that)

  • Rewrite history on several branches. From gitk it’s easy to checkout various branches, apply cherry-picks, reset branches to other commits and so on.

  • Look for commits that add or remove a given string and select only the changes made in one given file.

Behind the scenes, the -S option of git log is used.

By the way, gitk understands all the options git log does. So you can use: gitk -- src/foo to only show the commits in a given subdirectory for instance.

git-gui

I use git-gui when I know I left things in the files I do not want to be part of the next commit: debug logs, comments, …

I like the fact that you can select big hunks or small lines in a very intuitive way.

I also use the ‘revert changes made to this file’ (ctrl-j by default) feature a lot, because I’m looking directly at the changes that would be lost, so I feel more confident about not overwriting something important.

Apart from that, I’ve added a few configuration options to have more actions available in the top menu:

[guitool "pull-rebase"]
	cmd = git pull --rebase

[guitool "clean"]
	cmd = git clean -fd
	confirm = true

[guitool "reset"]
	cmd = git reset --hard
	confirm = true

Note how I have confirm = true for the “dangerous” operations, so that git-gui will display a pop-up for confirmation beforehand.

The last one is to activate spell checking for English when writing the commit message:

[gui]
	spellingdictionary = en_US

I have a similar configuration for Neovim:

augroup spell
  autocmd!
  autocmd filetype gitcommit  :setlocal spell spelllang=en
augroup end

Neovim

The last piece of the puzzle is the interaction with Neovim.

I use Tim Pope’s vim-fugitive for this.

It has tons of features.

I use it to display a current branch in my status line:

set statusline=%{VimBuddy()}\ [%n]\ %<%f\ %{fugitive#statusline()}%h%m%r%=%-14.(%l,%c%V%)\ %P\ %a

Yup, you can configure your status line by just setting a variable, no need for dedicated plugins …2

Note that most of the commands only work if fugitive detects that you are editing a file from a git repository.

Here are the commands I use the most, followed by the effect they have assuming I’m editing a file named foo.c:

  • :Gwrite run git add foo.c
  • :Gread: restore contents of foo.c from the latest commit (aka: undo all unstaged changes)
  • :Gmove foo2.c: run git mv foo.c foo2.c, and switch to foo2.c buffer without telling you “foo.c is no longer available”) 3
  • :Gdiff: show the differences made in foo.c. By default, the starting point is the current branch, but you can use :Gdiff origin/master to select a different starting point for instance.
  • :Gblame: run git blame foo.c, and when pressing ‘Enter’ when the cursor is at the end of line, show the details of the matching commit.
  • :Ggrep: same as :grep, but use the built-in git grep command. Since there are (rare) occasions when I’m not in a git repository, I tend to use Ag.vim too.
  • :Gcd: exactly the same effect as the gcd command described earlier :)

Conclusion

git takes quite some time to learn, but also offers tons of way to customize its behavior.

I hope I’ve given you an idea of everything that is possible.

Until next time!


  1. I tried to use Neovim directly as a git mergetool, but I find it too much confusing. [return]
  2. The VimBuddy() part can be seen in action on asciinema [return]
  3. By the way, the ‘:Move’ command from Tim Pope’s vim-eunuch does the same thing. [return]

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