Powerline-style PS1 written in pure Bash. Requires the Powerline-patched fonts. Why not just use Powerline, you ask? Well, I was using it on my NAS and it takes around 1500ms for the prompt to appear when the system is idle, but when doing something like compiling, it can take 5-15 seconds.

ps1.sh

#!/bin/bash

soft_sep='';
hard_sep='';

reset='\[\033[0m\]';
txt='\[\033[38;5;252m\]';
txt_prf='\[\033[38;5;252m\]';
user_bg='\[\033[48;5;31m\]';
root_bg='\[\033[48;5;31m\]';
host_colour='\[\033[48;5;166m\033[38;5;221m\]';
host_sepc='\[\033[38;5;166m\]';
user_colour='\[\033[1;48;5;31m\]'$txt;
user_sepc='\[\033[48;5;240m\033[38;5;31m\]';
root_colour='\[\033[1;48;5;52m\]'$txt;
root_sepc='\[\033[48;5;240m\033[38;5;52m\]';
bold='\[\033[1m\]';
git_clean_colour='\[\033[48;5;23m\]';
git_clean_sepc='\[\033[38;5;23m\]';
git_needs_commit_colour='\[\033[48;5;52m\]';
git_needs_commit_sepc='\[\033[38;5;52m\]';
path_colour='\[\033[0m\]'$user_sepc$txt;
cdir_sep=$reset'\[\033[38;5;240m\]';
pwd_sepc='\[\033[38;5;240m\]';

if [ $(id -u) == 0 ]; then
    user_bg=$root_bg;
    user_colour=$root_colour;
    user_sepc=$root_sepc;
fi

function __generate_ps1 {
    local prompt='';
    if [ "$SSH_CONNECTION" ]; then
        prompt+=$host_colour'  \h '$host_sepc$user_bg$hard_sep;
    fi

    prompt+=$user_colour' \u '"$user_sepc$hard_sep $path_colour";
    local git=$(git rev-parse --show-toplevel 2> /dev/null);
    local parts;
    local pwd=$(pwd);
    local path=${pwd/$HOME/\~};
    local git_colour=$git_clean_colour;
    local git_sepc=$git_clean_sepc;

    if [ $path == "/" ] || [ $path == "~" ]; then
        prompt+="$bold$path $reset$pwd_sepc$hard_sep$reset";
        export PS1=$prompt' ';
        return 0;
    fi

    if [[ "$git" ]]; then
        echo `git status` | grep "nothing to commit" > /dev/null 2>&1;
        if [[ "$?" != "0" ]]; then
            git_colour=$git_needs_commit_colour;
            git_sepc=$git_needs_commit_sepc;
        fi

        if [[ $git == '.' ]]; then
            path='';
            IFS='/' read -a parts <<< "${pwd/$HOME/\~}"; 
        else
            path=${pwd/$git};
            IFS='/' read -a parts <<< "${git/$HOME/\~}"; 
        fi

        local prnt=${parts[${#parts[@]}-2]};
        if [[ "$prnt" == "~" ]]; then
            prompt+="~ $soft_sep ";
        elif [[ "$prnt" ]]; then
            prompt+="… $soft_sep ";
        fi

        local branch=$(git rev-parse --abbrev-ref HEAD 2> /dev/null);
        prompt+="${parts[${#parts[@]}-1]} $git_colour$pwd_sepc$hard_sep$txt";
        prompt+="  $bold${branch/HEAD/master} $reset$git_colour";
    fi
    IFS='/' read -a parts <<< "$path"; 

    if [[ "$path" != '' ]]; then
        if [[ "$git" == '' ]]; then
            if [[ "${parts[2]}" ]] && [[ "${parts[3]}" ]]; then
                prompt+="… $soft_sep ";
            elif [[ "${parts[2]}" ]] && ( [[ "$path" == /* ]] || [[ "$path" == ~* ]] ); then
                prompt+="${path:0:1} $soft_sep ";
            elif [[ "$path" == /* ]]; then
                prompt+="/ $soft_sep ";
            fi
        else
            prompt+="$soft_sep ";
        fi
        [[ ${parts[${#parts[@]}-2]} ]] && prompt+="${parts[${#parts[@]}-2]} $soft_sep ";
        prompt+=$bold${parts[${#parts[@]}-1]}' ';
    fi

    if [[ $git ]]; then
        prompt+=$reset$git_sepc$hard_sep$reset;
    else
        prompt+=$reset$pwd_sepc$hard_sep$reset;
    fi

    prompt+=$reset' ';
    export PS1=$prompt;
}
export -f __generate_ps1
export PROMPT_COMMAND='__generate_ps1';

I'm not really a bash scriptwriter (if you couldn't tell), so there might be some ways of refactoring the code to be a little better. If so, let me know, I'm happy to learn.