Set up bash prompt to show vi-mode status, nix-shell, (colored) git status, and exit status. Excerpt from https://github.com/crvdgc/home-manager

.bashrc

# download git-prompt.sh from
# https://github.com/git/git/raw/master/contrib/completion/git-prompt.sh
# put it into ~/.git-prompt.sh
source ~/.git-prompt.sh

# Colors
RESET_COLOR='\[\e[0m\]'

BRIGHT_BLACK='\[\e[30;1m\]'
RED='\[\e[31m\]'
# GREEN='\[\e[32m\]'
# YELLOW='\[\e[33m\]'
# BLUE='\[\e[34m\]'
DIRBLUE='\[\e[34;1m\]' # blue as is used by dircolors for dirs
CYAN='\[\e[36m\]'
GRAY='\[\e[37;0m\]'

function color() {
  echo "$*${RESET_COLOR}"
}

function set_bash_prompt() {
  declare -ri exit_status="$?"

  declare -r username='\u'
  declare -r hostname='\h'
  declare -r working_dir='\w'

  declare exit_status_pr
  if [[ "${exit_status}" -ne 0 ]]; then
    exit_status_pr="[$(color "${RED}${exit_status}")]"
  else
    exit_status_pr=''
  fi

  declare username_pr
  if [[ -n "$IN_NIX_SHELL" ]]; then
    username_pr="$(color "${BRIGHT_BLACK}[nix-shell]")"
  else
    username_pr="$(color "${CYAN}${username}")"
  fi

  declare hostname_pr
  hostname_pr="$(color "${CYAN}${hostname}")"

  declare working_dir_pr
  working_dir_pr="$(color "${DIRBLUE}${working_dir}")"

  export GIT_PS1_DESCRIBE_STYLE='branch'
  export GIT_PS1_SHOWCOLORHINTS='y'
  export GIT_PS1_SHOWDIRTYSTATE='y'
  # export GIT_PS1_SHOWSTASHSTATE='y'
  export GIT_PS1_SHOWUNTRACKEDFILES='y'
  export GIT_PS1_SHOWUPSTREAM='auto'

  __git_ps1 "${username_pr}@${hostname_pr}:${working_dir_pr}" "${exit_status_pr} $ "
}

PROMPT_COMMAND=set_bash_prompt

.inputrc

# https://wiki.archlinux.org/index.php/Readline
set editing-mode vi
set show-mode-in-prompt on
set vi-ins-mode-string \1\e[34;1m\2[I]\1\e[0m\2
set vi-cmd-mode-string \1\e[33;1m\2[N]\1\e[0m\2