bash/zsh git prompt support

Clone From https://github.com/git/git/tree/master/contrib/completion

This script allows you to see the current branch in your prompt.

To enable:

1. Copy this file to somewhere (e.g. ~/.git-prompt.sh).

2. Add the following line to your .bashrc/.zshrc:

   source ~/.git-prompt.sh 3a) Change your PS1 to call __git_ps1 as

   command-substitution: Bash: PS1='[\u@\h \W$(__git_ps1 " (%s)")]$ ' ZSH: PS1='[%n@%m %c$(__git_ps1 " (%s)")]$ ' the optional argument will be used as format string. 3b) Alternatively, if you are using bash, __git_ps1 can be used for PROMPT_COMMAND with two parameters, <pre> and <post>, which are strings you would put in $PS1 before and after the status string generated by the git-prompt machinery.
   e.g. PROMPT_COMMAND='__git_ps1 "\u@\h:\w" "\\\$ "' will show username, at-sign, host, colon, cwd, then various status string, followed by dollar and SP, as your prompt. Optionally, you can supply a third argument with a printf format string to finetune the output of the branch status

Additional:

The argument to __git_ps1 will be displayed only if you are currently in a git repository. The %s token will be the name of the current branch.

In addition, if you set GIT_PS1_SHOWDIRTYSTATE to a nonempty value, unstaged (*) and staged (+) changes will be shown next to the branch name. You can configure this per-repository with the bash.showDirtyState variable, which defaults to true once GIT_PS1_SHOWDIRTYSTATE is enabled.

You can also see if currently something is stashed, by setting GIT_PS1_SHOWSTASHSTATE to a nonempty value. If something is stashed, then a '$' will be shown next to the branch name.

If you would like to see if there're untracked files, then you can set GIT_PS1_SHOWUNTRACKEDFILES to a nonempty value. If there're untracked files, then a '%' will be shown next to the branch name. You can configure this per-repository with the bash.showUntrackedFiles variable, which defaults to true once GIT_PS1_SHOWUNTRACKEDFILES is enabled.

If you would like to see the difference between HEAD and its upstream, set GIT_PS1_SHOWUPSTREAM="auto". A "<" indicates you are behind, ">" indicates you are ahead, "<>" indicates you have diverged and "=" indicates that there is no difference. You can further control behaviour by setting GIT_PS1_SHOWUPSTREAM to a space-separated list of values:

verbose       show number of commits ahead/behind (+/-) upstream
legacy        don't use the '--count' option available in recent
              versions of git-rev-list
git           always compare HEAD to @{upstream}
svn           always compare HEAD to your SVN upstream

By default, __git_ps1 will compare HEAD to your SVN upstream if it can find one, or @{upstream} otherwise. Once you have set GIT_PS1_SHOWUPSTREAM, you can override it on a per-repository basis by setting the bash.showUpstream config variable.

If you would like to see more information about the identity of commits checked out as a detached HEAD, set GIT_PS1_DESCRIBE_STYLE to one of these values:

contains      relative to newer annotated tag (v1.6.3.2~35)
branch        relative to newer tag or branch (master~4)
describe      relative to older annotated tag (v1.6.3.1-13-gdd42c2f)
default       exactly matching tag

If you would like a colored hint about the current dirty state, set GIT_PS1_SHOWCOLORHINTS to a nonempty value. The colors are based on the colored output of "git status -sb".