Getting error: bash: parse_git_branch: command not found

The problem is that parse_git_branch is defined in .bash_profile, but not exported. When you run sudo bash, it starts an nonlogin shell that sources .bashrc instead of .bash_profile. PS1 was exported and so is defined in the new shell, but parse_git_branch is not.

Typically, you would define both PS1 and parse_git_branch in .bashrc and export neither of them. macOS is a little different from Linux, in that a terminal emulator starts a login shell instead of an ordinary interactive shell. A good practice is to put the definitions in .bashrc, then source .bashrc from .bash_profile.

Here's how I would split up your existing .bash_profile:

In .bashrc:

parse_git_branch() {
    git branch 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/ (\1)/'
}

PS1="\u@\h \[\033[32m\]\w - \$(parse_git_branch)\[\033[00m\] $ "

[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm" # Load RVM$

if [ -f ~/.git-completion.bash ]; then
  . ~/.git-completion.bash
fi

In .bash_profile:

# Many of the paths you were adding to PATH should already be
# there in the default configuration; run /usr/lib/path_helper
# to see the default.
PATH=/Applications/XAMPP/xamppfiles/bin:/usr/local/sbin:$PATH
export EDITOR='subl -w'
export JAVA_HOME=$(/usr/libexec/java_home)

[[ -f ~/.bashrc ]] && source ~/.bashrc

What fixed the issue in my case was adding the hashbang (#!/bin/bash - or could be tcsh in the end in your case) to the beginning of my .bashrc.

Without hashbang at the top of .bashrc the function still applied to PS1 but only within the main partition (on my SSD), but when I tried to manipulate git repositories on another mount (an extra HDD) I had this message.

So just adding #!/bin/bash and then reloading .bashrc (by doing source ~.bashrc) fixed this issue for me.

By looking at your .bash_profile, it seems you have forgotten to add the keyword function before parse_git_branch() {}

Try changing to,

function parse_git_branch() {
git branch 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/ (\1)/'
}

After that, reload your .bash_profile and see if it works.

Reference: Functions in Bash.