script to show git branch in bash no longer works on ubuntu 18.04

Although you already solved the problem, I'd like to introduce the solution already shipped with git:

Together with git the file /usr/lib/git-core/git-sh-prompt gets installed. Years ago it was in the contrib directory but meanwhile it made it into the official paths. The file isn't meant to be executed (in fact, it doesn't have x flags) but rather to be sourced from the .bashrc. It defines some functions to handle a pretty prompt, the most prominent being __git_ps1.

You can add the following lines to your .bashrc:

source /usr/lib/git-core/git-sh-prompt
export PS1="${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u:\[\033[01;34m\]\w\[\033[00m\]\$(__git_ps1)\[\033[00m\] $ "

The top of the file /usr/lib/git-core/git-sh-prompt gives some description of what else can be done. My version says 1) Copy this file to somewhere (e.g. ~/.git-prompt.sh). but this is not necessary (the instruction is obsolete).

You may also set some environment variables to alter the function's behaviour. I, for instance, use

export GIT_PS1_SHOWDIRTYSTATE=yes

The result then looks like:

# clean
pduck:~/oss/rsyslog (master) $ 

or

# dirty
pduck:~/oss/rsyslog (master *) $ 

or

# something added to index
pduck:~/oss/rsyslog (master +) $ 

or

# in a completely fresh repo
pduck:~/oss/xxx (master #) $ 

---

Btw: The "proper" way to get the current branch is not to parse git branch's output as that may change with new git versions. git branch is a so-called porcelain command which means its output is nice and pretty but not guaranteed to stay the same with different versions. The git guys thus recommend plumbing tools for scripting. With plumbing the current branch can be determined with

if [ "$(git rev-parse --is-inside-work-tree 2>/dev/null)" = "true" ]; then
    current_branch=$(git symbolic-ref --quiet --short HEAD || git rev-parse --short HEAD)
else
    current_branch=""
fi

The first assignment works if HEAD is a symbolic reference (that is: a branch or tag is checked out). If you checked out something that has no label (e.g. git checkout HEAD^^), then it fails and we use git rev-parse --short HEAD instead to show the SHA1. The if checks whether we are in a git working directory at all (because else the commands don't make any sense).

The solution was quite simple.

I set an upstream, staged a commit and pushed it. After that it worked.

I thought that the script somehow used the .git folder that is generated with git init. Since it works on branches that does not have an upstream.