rod mclaughlin

Gradually Getting Git (25 dec 13)

Not everyone would spend Christmas Day learning a source control system, but I'm not everyone.

Based on this superb and brief explanation of Git's power, I'm learning how to REBASE:

http://ftp.newartisans.com/pub/git.from.bottom.up.pdf

In a nutshell, this is what rebase does:

Suppose you have two branches of the same project, foo and bar (created by simply typing 'git branch foo' or 'git branch bar')

start - foo1 - foo2 - foo3
                 \
                 bar1 - bar2 - bar3

I'm not ready to merge bar back into the main branch, foo. But I am aware that people are working on foo too, and files might be getting more and more divergent, meaning when we do merge, it'll be harder. What I do, is 'rebase'. This makes MY branch look as if I started it by branching off of the LATEST commit in foo, which is foo3, rather than the earlier commit, foo2. So my local branch, bar, will end up looking like this:

start - foo1 - foo2 - foo3 - bar1 - bar2 - bar3

This makes it simpler to merge, especially if there are many branches. This is how the Linux kernel is maintained, for example.

Rebasing sometimes requires 'resolving conflicts'.

For example, suppose I DELETE a file in branch bar, and someone else CHANGES it in branch foo. What happens when I rebase, bar onto foo?  

# I DO THIS:
$ git checkout bar
$ git rebase foo
# THIS IS WHAT GIT SAYS:
First, rewinding head to replay your work on top of it...
Applying: Adding modified bar which was deleted in branch 
foo to see what happens when we rebase
Using index info to reconstruct a base tree...
A    bar.rb
<stdin>:10: trailing whitespace.
# This class was deleted on branch foo, but edited on branch bar, 
to see what happens when we try to rebase 
warning: 1 line adds whitespace errors.
Falling back to patching base and 3-way merge...
CONFLICT (modify/delete): bar.rb deleted in HEAD and modified in 
Adding modified bar which was deleted in branch foo to see what happens 
when we rebase. 
Version Adding modified bar which was deleted in branch foo to 
see what happens when we rebase of bar.rb left in tree.
Failed to merge in the changes.
Patch failed at 0001 Adding modified bar which was deleted in branch foo to see 
what happens when we rebase
The copy of the patch that failed is found in:
   bar/.git/rebase-apply/patch
When you have resolved this problem, run "git rebase --continue".
If you prefer to skip this patch, run "git rebase --skip" instead.
To check out the original branch and stop rebasing, run "git rebase --abort".

It's better to deal with this now rather than later:

$ git rebase --abort
$ git rebase -i foo

Refer to http://ftp.newartisans.com/pub/git.from.bottom.up.pdf for what to do next.

Portland

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