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====== GIT - The Stupid Content Tracker ======

Here are some thoughts about ''git''. No basic stuff, mostly best practices I
discovered by (and for) myself.

===== Juggling Around Remotes =====

Assume a local project named //proj// and a new remote clone at
[git://bla.org/proj.git]. First add the new remote:

  ~/git/proj % git remote add bla git://bla.org/proj.git

see what you've got:

  ~/git/proj % git remote show bla

next, do an initial fetch of the remote's content:

  ~/git/proj % git fetch bla

see the remote's branches:

  ~/git/proj % git br -r | grep bla/

assuming bla is upstream and you have local commits to apply on top of it,
first rebase your local master onto bla/master, changing the history of your
local branch:

  ~/git/proj % git rebase bla/master master

then you can fast-forward push the new local patches:

  ~/git/proj % git push bla master:master;

assuming you are upstream and bla has published commits to apply on top of
yours, you can first check if the remote's master is up to date:

  ~/git/proj % git log bla/master..master

the commits you see in the log (if any) are the changes contained in your
local master, but not in bla/master. If there are none, there is no need for
merging, pulling from the remote branch will result in a fast-forward. Next,
check what the remote has for us:

  ~/git/proj % git log master..bla/master

depending on the amount of commits and personal taste of course, there are
several options to apply the remote commits to one's local branch. E.g. one
can pick them one by one:

  ~/git/proj % git cherry-pick <commit-id>

or simply merge the branch into yours:

  ~/git/proj % git merge bla/master


===== Editing History =====

The following stuff is not meant for published clones as those should keep
their history consistent. But it's very useful for local development,
especially housekeeping tasks such as fixing up buggy commits in the past.


==== Dropping A Past Commit ====

The command seems easy:

  ~/git/proj % git rebase --onto <commit-id-A> <commit-id-B>

the trick is getting the commit-ids right:

 * **commit-id-A** is the last commit before the one to be dropped
 * **commit-id-B** is the actual commit to be dropped

so in a history like this:

  A--B--C--D

issuing the following command:

  ~/git/proj % git rebase --onto B C

will lead to this:

  A--B--D

you can even skip a row of commits:

  ~/git/proj % git rebase --onto B D

and you get:

  A--D

==== Editing Past Commits ====

I use a temporary branch for these things:

  ~/git/proj % git branch hist <commit-to-change>

do your stuff and amend the commit:

  ~/git/proj % git checkout hist
  ~/git/proj % vim bla blub
  ~/git/proj % git commit -a --amend

finally rebase the original branch on top of hist and drop the temporary
branch:

  ~/git/proj % git rebase hist master
  ~/git/proj % git branch -d hist

note that conflicts here are quite common, especially for the first commit
from master being applied by ''git rebase'', as in fact that's the commit
which has been corrected and should be dropped.

===== Cloning via SSH =====

Using SSH as transport is trivial, as it's widely used for repositories with
write access. The URL to use for ''git clone'' or ''git remote'' looks like
this:

  ssh://[user@]example.com[:port]/path/to/repo.git/

An alternative, "scp-like" syntax is supported as well:

  [user@]example.com:path/to/repo.git/

==== Specifying the SSH Identity ====

Sometimes it's not sufficient to clone via SSH and relying upon the first
accepted key in ''ssh-agent''. A practical example is having multiple accounts
in Github - like with ''gitolite'', all users connect using a common username
and are distinguished based on pubkey. This may be given during clone like so, according to a popular answer on [[https://stackoverflow.com/a/41947805|StackOverflow]]:

  git clone -c core.sshCommand="/usr/bin/ssh -i /home/me/.ssh/id_rsa_foo" git@github.com:me/repo.git

Or fixed after the fact in the local repo's config:

  git config --local core.sshCommand "/usr/bin/ssh -i /home/me/.ssh/id_rsa_foo"