git 执行git push 和git pull的操作时候，可能会失败，并有如下的两种英文提示：
1、You asked me to pull without telling me which branch you want to merge with, and 'branch.dev.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 "dev"]
remote = <nickname>
merge = <remote-ref>
[remote "<nickname>"]
url = <url>
fetch = <refspec>
See git-config(1) for details.
在高版本的 git下面，也许会看见这样的提示：
2、 There is no tracking information for the current branch.
Please specify which branch you want to merge with.
See git-pull(1) for details
git pull <remote> <branch>
If you wish to set tracking information for this branch you can do so with
git branch --set-upstream master origin/<branch>
解决方案：指定当前工作目录工作分支，跟远程的仓库，分支之间的链接关系。
比如我们设置master对应远程仓库的master分支
git branch --set-upstream master origin/master
这样在我们每次想push或者pull的时候，只需要 输入git push 或者git pull即可。
在此之前，我们必须要指定想要push或者pull的远程分支。
git push origin master
git pull origin master.