my take for a simple shell prompt

prompt.sh

# run the prompt after every command.
PROMPT_COMMAND=prompt_command_hook

function prompt_command_hook()
{
	# get the current branch in the format (branch)
	GIT_BRANCH=$(__git_ps1 "(%s)")

	# if the branch is null, only display user, pwd
	# else add an @ and the branch
	if [[ -z "$GIT_BRANCH" ]]; then
		PS1='┌\e[0;92m[\u] \e[0;36m$(get_pwd)\n\e[0m└$ '
	else
		PS1='┌\e[0;92m[\u] \e[0;36m$(get_pwd)\e[0;37m@\e[0;95m$GIT_BRANCH\n\e[0m└$ '
	fi
}

function get_pwd() {
	# set default variables
	CURRENT_DIR="${PWD/"$HOME"/"~"}"	
	LENGTH=${#CURRENT_DIR}
	MAX_LENGTH=20

	# if the current_directory is smaller than the max length 
	# then echo the dir and exit.
	if [[ $LENGTH -le $MAX_LENGTH ]]; then
		echo $CURRENT_DIR
		exit
	fi

	# split the path into directories. 
	IFS="/" read -r -a SPLIT_DIRECTORIES <<< $CURRENT_DIR

	# if the directory only has one or less subdirectory just
	# return the current directory. 
	if [[ ${#SPLIT_DIRECTORIES[@]} -le 1 ]]; then
		echo $CURRENT_DIR 
		exit
	fi

	# set the tmp_dir variable to the last directory in the array 
	# and set the current_dir to tmp_dir.
	# loop backwards though the directory array starting from the
	# second to last element in the array.
	TMP_DIR="${SPLIT_DIRECTORIES[-1]}"
	CURRENT_DIR=$TMP_DIR
	for (( idx=${#SPLIT_DIRECTORIES[@]} - 2; idx >= 0; idx-- )); do
		# add the current element to the existing directory.
		TMP_DIR="${SPLIT_DIRECTORIES[idx]}/$TMP_DIR"

		# if the last added directory is the home directory
		# return with the ~ regardless if it is "too long".
		# else if the newly created directory is too long return the last 
		# directory with '.../' as prefix.
		if [[ "${SPLIT_DIRECTORIES[idx]}" = "~" ]]; then
			echo "~/$CURRENT_DIR"
			exit
		elif [[ ${#TMP_DIR} -gt $(( $MAX_LENGTH - 4 )) ]]; then
			echo ".../$CURRENT_DIR"
			exit
		fi

		# set the current_directory to the new tmp_dir.
		CURRENT_DIR=$TMP_DIR
	done
}