Git branch in your bash prompt

Today while googling for answers to question ‘How to check if Git is installed from bash’ stumbled upon this stackoverflow question How to check if Git is installed from .bashrc. Having branch name in your bash prompt seems like a great idea especially if you are using git all the time. Recently I have been using git for my personal projects, from time to time I issue command

git status

just to check what branch I am on. I immediately started questioning myself where does this __git_ps1 come from, some more googling unearthed this article Configuring Git, which mentions that __git_ps1 becomes available after you install git. Kinda makes sense, but still does not answer where it is coming from. After more searching I came across this git related thread - bash-completion now loads completions dynamically, so __git_ps1 is not defined when you open a shell. After all __git_ps1 is an extension to bash completion that you can find here

/usr/lib/git-core/git-sh-prompt

found it while reading - An introduction to bash completion: part 1 from Debian Administration - Debian Administration Resources which is a great resource on this topic and on Debian administration in general, for me bash completion is not completely new concept, but I have not ever thought about adding any extensions to be honest.