版本控制 - git创建分支失败，无法提交，难以理解分支的用途

疑惑

对git分支不了解，今天测试使用git分支，本地创建了一个 new分支，commit后push报错了，且远程并没有看到new分支。

截图

远程截图bitbucket.org，只看到默认的master分支，看不到new分支

命令

Welcome to Git (version 1.9.5-preview20141217)


Run 'git help git' to display the help index.
Run 'git help ' to display help for specific commands.

Administrator@NSGRZQBMHMHTYQF /E
$ mkdir test

Administrator@NSGRZQBMHMHTYQF /E
$ cd test

Administrator@NSGRZQBMHMHTYQF /E/test
$ touch "d" > 1.txt

Administrator@NSGRZQBMHMHTYQF /E/test
$ ls
1.txt  d

Administrator@NSGRZQBMHMHTYQF /E/test
$ git init
Initialized empty Git repository in e:/test/.git/

Administrator@NSGRZQBMHMHTYQF /E/test (master)
$ git status
On branch master

Initial commit

Untracked files:
  (use "git add ..." to include in what will be committed)

        1.txt
        d

nothing added to commit but untracked files present (use "git add" to track)

Administrator@NSGRZQBMHMHTYQF /E/test (master)
$ git add --all

Administrator@NSGRZQBMHMHTYQF /E/test (master)
$ git commit -m "head version"
[master (root-commit) 22a9e38] head version
 2 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 1.txt
 create mode 100644 d

Administrator@NSGRZQBMHMHTYQF /E/test (master)
$ git remote add origin git@bitbucket.org:myacc/br.git

Administrator@NSGRZQBMHMHTYQF /E/test (master)
$ git push -u origin --all # pushes up the repo and its refs for the first time
Counting objects: 3, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (3/3), 214 bytes | 0 bytes/s, done.
Total 3 (delta 0), reused 0 (delta 0)
To git@bitbucket.org:myacc/br.git
 * [new branch]      master -> master
Branch master set up to track remote branch master from origin.

Administrator@NSGRZQBMHMHTYQF /E/test (master)
$ git branch new

Administrator@NSGRZQBMHMHTYQF /E/test (master)
$ git checkout new
Switched to branch 'new'

Administrator@NSGRZQBMHMHTYQF /E/test (new)
$ git status
On branch new
nothing to commit, working directory clean

Administrator@NSGRZQBMHMHTYQF /E/test (new)
$ touch "2" > 2.txt

Administrator@NSGRZQBMHMHTYQF /E/test (new)
$ git status
On branch new
Untracked files:
  (use "git add ..." to include in what will be committed)

        2
        2.txt

nothing added to commit but untracked files present (use "git add" to track)

Administrator@NSGRZQBMHMHTYQF /E/test (new)
$ git add --all

Administrator@NSGRZQBMHMHTYQF /E/test (new)
$ git status
On branch new
Changes to be committed:
  (use "git reset HEAD ..." to unstage)

        new file:   2
        new file:   2.txt


Administrator@NSGRZQBMHMHTYQF /E/test (new)
$ git commit -m "branch new head version"
[new 4429a97] branch new head version
 2 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 2
 create mode 100644 2.txt

Administrator@NSGRZQBMHMHTYQF /E/test (new)
$ git push -u origin:new
warning: push.default is unset; its implicit value is changing in
Git 2.0 from 'matching' to 'simple'. To squelch this message
and maintain the current behavior after the default changes, use:

  git config --global push.default matching

To squelch this message and adopt the new behavior now, use:

  git config --global push.default simple

When push.default is set to 'matching', git will push local branches
to the remote branches that already exist with the same name.

In Git 2.0, Git will default to the more conservative 'simple'
behavior, which only pushes the current branch to the corresponding
remote branch that 'git pull' uses to update the current branch.

See 'git help config' and search for 'push.default' for further information.
(the 'simple' mode was introduced in Git 1.7.11. Use the similar mode
'current' instead of 'simple' if you sometimes use older versions of Git)

ssh: Could not resolve hostname origin: no address associated with name
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

Administrator@NSGRZQBMHMHTYQF /E/test (new)
$ git status
On branch new
nothing to commit, working directory clean

对分支的理解

1.创建了分支之后，再 git add . 就添加了，然后git commit -m ""就提交到了当前的分支？
2.如果运行了 git checkout new，那么是不是会从远程下载new分支到本地，直接自动合并？
3.如果运行了 git checkout new，然后关闭git bash再打开git bash，默认的就是new分支了
4.git 默认的分支就是master分支？

分支的用途

假如开发ubuntu，A程序员在开发LTS12.04分支，然后B程序员却继续开发 V13 版本？
然后某一次B程序员需要去帮A程序员开发LTS12.04，那B应该先将项目V13的所有文件git push V13分支，再 git checkout LTS12.04，再git pull拉取所有的LTS12.04分支。修改后，再git push LTS12.04分支，再checkout V13分支，再 git pull V13所有程序，才返回到了V13的分支？
是这样吗？但git pull不是合并了B项目文件夹下的V13和LTS12.04两个版本的代码了吗

难以理解……