git pull没有指定branch的报错

执行git pull或者git push的时，有时候会出现如下报错：

$ git pull
You asked me to pull without telling me which branch you
want to merge with, and 'branch.linux_c++.merge' in
your configuration file does not tell me, either. Please
specify which branch you want to use on the command line and
try again (e.g. 'git pull <repository> <refspec>').
See git-pull(1) for details.

If you often merge with the same branch, you may want to
use something like the following in your configuration file:

    [branch "linux_c++"]
    remote = <nickname>
    merge = <remote-ref>

    [remote "<nickname>"]
    url = <url>
    fetch = <refspec>

See git-config(1) for details.

我们先来看看当前分支状态：

$ git branch -av
* linux_c++                584efea add cscope and fix fileencoding problam
  master                   ee9d037 v1.0.1: add install.sh
  remotes/origin/HEAD      -> origin/master
  remotes/origin/linux_c++ 584efea add cscope and fix fileencoding problam
  remotes/origin/master    ee9d037 v1.0.1: add install.sh

当前所在的linux_c++分支虽然与远程linux_c++同名，但实际上，这个分支并不是origin/linux_c++分支的追踪分支，所以当直接用git pull去请求拉新分支的时候，git并不知道应该拉取哪个分支。

因此，解决此问题有两个方案，一个是git pull或者git push的时候，指定相应的远程分支名，如：

$ git pull origin linux_c++

另一个方案则是，设置当前分支追踪某个远程分支。设置现有分支追踪远程分支的方式有两种：

git branch -u remote-name/branch_name branch_name

或者

git branch --set-upstream-to=remote_name/branch_name branch_name

当然，还可以再创建本地分支的时候，直接使其追踪到远程分支：

git checkout -b local_branch remote_name/remote_branch

当前我们的分支是已有分支，那么可以输入：

$ git branch -u origin/linux_c++ linux_c++
Branch linux_c++ set up to track remote branch linux_c++ from origin.

应当注意的一点是：git branch -u 和git branch --set-upstream-to 的两个选项都是要在较高的git版本才有，至少博主在1.7.1上发现没有这两个选项，而1.8.3.1上是有的。