Git
========================================

(2019)

The [Pro Git](https://git-scm.com/book/en/v2/) book is very helpful.
Its authors, Scott Chacon and Ben Straub, generously publish it under a Creative Commons license.

Git is a distributed version control system.
Branching and merging is far easier than with traditional VCS's.

	$ man git
	$ man gittutorial
	$ man git-help
	$ git help
	$ git help [commit add etc]

Create a new repo:

	$ cd myproject
	$ git init
	$ git add .
	$ git status
	$ git commit -em "Initial import."

Changes are added to a cache/staging area before being committed.
Files can be added individually before being committed as a second step, or the add-all-commit can be done as one step:

	$ git add foo.txt
	$ git status
	$ git commit
	$ git commit -aem 'Fixed caching (issue 4321).'

Keep the first line of the commit message short — fewer than fifty characters.
Include an additional details in subsequent paragraphs separated by a blank line.
The `-e` flag invokes the editor to compose a commit message:

	$ git commit -e

Pull the diffs for the staged changes directly into the commit message editor:

	$ git commit -v

`git-commit(1)` says:

> Note that this diff output doesn’t have its lines prefixed with #. This diff will not be a part of the commit message.

**Best of all:**

	$ git commit -ve

Unstage a file added to the cache but not yet committed:

	$ git rm --cached foo.txt

Revert a changed or deleted file:

	$ git checkout -- foo.txt

(A bare double-dash " -- " avoids ambiguity by separating options from a list of arguments.)

Discard all local working changes:

	$ git reset --hard HEAD


Remote Repositories
----------------------------------------

Create a remote origin repo:

	$ ssh example.com mkdir ~/repo/myproject
	$ ssh example.com git init --bare ~/repo/myproject
	$ cd myproject
	$ git remote add origin ssh://example.com/~/repo/myproject
	$ git push --set-upstream origin master

At some point `--set-upstream` stopped working.
Instead:

	$ git branch --set-upstream-to=origin/master master

Clone a remote repo:

	$ git clone ssh://example.com/project

Pull updates from a remote:

	$ git pull [remote]

Additional remotes:

	$ git remote -v
	$ git remote add mynewremote ssh://example.com/~/foo
	$ git push mynewremote

Add Github as an additional remote:

	$ curl -u 'pgorman' https://api.github.com/user/repos -d '{"name":"myproject","description":"This is my project."}'
	$ git remote add github https://github.com/pgorman/myproject.git
	$ git remote -v
	$ git push github master

Show status of a particular remote:

	$ git remote show <remote>

Unlink a remote repository:

	$ git remote remove github


Reviewing Logs and Comparing Changes
----------------------------------------

```
$  git log --stat

commit 47e95939843d35906c26032338727f98a901f7a2
Author: Paul Gorman <me@example.com>
Date:   Thu Aug 9 22:04:56 2018 -0400

    Spelling.

  zerapis.txt | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

commit c11ff2d1c0d1fe0f0f6e0634c503b0a917c8834e
Author: Paul Gorman <me@example.com>
Date:   Thu Aug 9 21:10:31 2018 -0400

    Moving to markdown.

  zerapis.txt | 277 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 277 insertions(+)

$  git log

commit 47e95939843d35906c26032338727f98a901f7a2
Author: Paul Gorman <me@example.com>
Date:   Thu Aug 9 22:04:56 2018 -0400

    Spelling.

commit c11ff2d1c0d1fe0f0f6e0634c503b0a917c8834e
Author: Paul Gorman <me@example.com>
Date:   Thu Aug 9 21:10:31 2018 -0400

    Moving to markdown.

$  git log  --pretty=oneline

47e95939843d35906c26032338727f98a901f7a2 Spelling.
c11ff2d1c0d1fe0f0f6e0634c503b0a917c8834e Moving to markdown.

$ git log --all --graph --oneline --decorate
* 2a33954 (HEAD -> master, origin/master) Server gives each game an ID.
* 6d73f85 Draw board by JS.
* 817fe58 Started Go web server.
* f579205 Tinkering with UI.
* 3aa1cd4 Visually indicate selected tool.
* ca1b186 Client-side stuff works.
* dcd844c Initial import.
```

Review commit logs, and compare two commits:

	$ git log --stat [master origin foo etc]
	$ git diff e274 47c9

Commits are identified by 40-hexadigit hashes. We can refer to a commit by the first few characters of the hash, where there's no ambiguity.

Show changes over time for a particular file:

	$ git log -p myfile

Search when a particular string changed (a.k.a., Git's "pickaxe" option):

	$ git log -S foobar

Diff changed files have not yet been staged/cached:

	$ git diff

Diff staged/cached files:

	$ git diff --cached

Diff HEAD with the previous commit:

	$ git diff @~..@
or:
	$ git diff HEAD\^ HEAD


Branches and Merging
----------------------------------------

Branches are named. The default branch is 'master'. The tag 'HEAD' refers to the tip (latest commit) of the current branch.

	$ git branch
	$ git branch --list
	$ git branch testbranch
	$ git checkout testbrach
	$ git checkout master
	$ git branch --delete testbranch

If we want to switch branches without committing the work-in-progress in our current branch:

	$ git stash
	$ git stash list

Restore stashed files once we switch back to the original work-in-progress brach:

	$ git stash list
	$ git stash apply [stash@{n}]

Merge a branch back into master:

	$ git checkout master
	$ git merge testbranch

Resolve merge conflicts:

	$ git mergetool

or specify the tool:

	$ git mergetool --tool=gvimdiff


Config Files
----------------------------------------

`~/.gitconfig` has per-user settings.

`/etc/gitconfig` is global for the box.

Show effective settings:

	$ git config --list --show-origin

`~/repo/myproject/.git/config` has per-project settings.

`~/repo/myproject/.gitignore` sets per-project list of files to ignore. Wildcards can be used.


Reviewing a Github merge request
----------------------------------------

https://help.github.com/articles/checking-out-pull-requests-locally/

1. Under the repository name, click Pull requests.
2. Select a pull request from the list of pull requests.
3. Near the bottom of the pull request, in the merge box, click "command line instructions". Follow the instructions.

For example:

Check out a new branch and test the changes:

	git checkout -b makhidkarun-master master
	git pull https://github.com/makhidkarun/travellercharactergenerator.git master

Merge the changes and update GitHub:

	git checkout master
	git merge --no-ff makhidkarun-master
	git push github master


Tagging
----------------------------------------

https://git-scm.com/book/en/v2/Git-Basics-Tagging

Tags mark specific points in a repo's history as important.
Use this to label a particular commit as a major version (v2.0), for example.

```
$ git tag
v1.0
v2.0

$ git tag -l "v1.8.5*"
v1.8.5
v1.8.5-rc0
v1.8.5-rc1
v1.8.5-rc2
v1.8.5-rc3
v1.8.5.1
v1.8.5.2
v1.8.5.3
v1.8.5.4
v1.8.5.5

$ git tag -a v2.0 -m "Release 2.0 finalizes the new network features."
```

Or, retroactively tag a previous commit:

```
$ git tag -a v1.2 9fceb02
```

By default, git does not push tags to remote servers.
Push one or all tags like:

```
$ git push origin v1.5
$ git push origin --tags
```


Not Covered
----------------------------------------

rebase, tags, blame, pickaxe, bisect


Links
----------------------------------------

- http://git-scm.com/book/en/v2
- http://ohshitgit.com/
- https://bitbucket.org/BitPusher16/dotfiles/raw/49a01d929dcaebcca68bbb1859b4ac1aea93b073/refs/git/git_examples.sh
- https://girliemac.com/blog/2017/12/26/git-purr/