bash_prompt

#!/bin/bash
# build a fancy bash prompt with dynamic color
# (the shebang is only there to get vim to use bash syntax highlighting)

# debug helper
#trace() { echo "$@" 1>&2; }

# ansi styling
# following the advice of http://mywiki.wooledge.org/BashFAQ/037
# with some help from http://wiki.bash-hackers.org/scripting/terminalcodes
# todo maybe define more colors like http://mediadoneright.com/content/ultimate-git-ps1-bash-prompt
RESET=$(tput sgr0)
BOLD=$(tput bold)
NOBOLD=$(tput rmso)

BLACK=$(tput setaf 0)
RED=$(tput setaf 1)
GREEN=$(tput setaf 2)
YELLOW=$(tput setaf 3)
BLUE=$(tput setaf 4)
MAGENTA=$(tput setaf 5)
CYAN=$(tput setaf 6)
WHITE=$(tput setaf 7)
PLAIN=$(tput setaf 9)


# /home/username/foo -> ~/foo
function unexpand_home_tilde() {
    # add trailing slash to distinguish from /home/usernameOFSOMEONEELSE
    local here=$1/
    # substitute ~/ for $HOME/ 
    local friendly=${here/$HOME\//\~\/}
    # remove the trailing slash before emitting
    friendly=${friendly/%\/}
    echo $friendly
}

# decide what color a path should be based on some attributes about it
# echos an ANSI sequence
function color_for_path() {
    # default color
    local dircolor=$BOLD$BLUE
    local here="$1"
    local perms=$(stat --format=%a "$here")
    if [[ -L $here ]]; then
        # dir is a symlink
        dircolor=$BOLD$CYAN
    elif [[ "$perms" -eq 700 ]]; then
        # private-only dir
        dircolor=$MAGENTA
    elif [[ "$perms" -eq 777 ]]; then
        # world-writable dir
        dircolor=$YELLOW
    elif [[ ! -w "$here" ]]; then
        # dir not writable for me
        dircolor=$RESET
    fi
    # TODO any other cases?  non-owned dir?  group-writable dir?
    # sticky bits?  (stat returns 1777 for /tmp)
    echo "$dircolor"
}


# echos a path with each segment individually colorized
# also inserts \[ \] sequences, for use in $PS1
function colorize_path_segments() {
    local path="$(unexpand_home_tilde "$1")"
    IFS='/' read -ra segs <<< "$path"

    local accum=""
    local output=""

    for seg in "${segs[@]}"; do
        if [[ $seg == '~' ]]; then
            accum=$HOME
        else
            accum="$accum/$seg"
        fi
        local col=$(color_for_path "$accum")
        output="\[$RESET\]$output\[$RESET$col\]$seg\[$BOLD$BLUE\]/"
    done

    # remove trailing slash
    output=${output/%\/}
    echo "$output\[$RESET\]"
}



######################################################################
# Initialize a series of variables, related to prompt config
# these are static for the life of a shell
case "$USER" in
    nathan|nstien|npstien|Nathan|"Nathan Stien") 
        usercolor=$GREEN
        terminator=∫
        ;;
    root|Administrator) 
        usercolor=$BOLD$RED;
        terminator='#'
        ;;
    *)
        usercolor=$BOLD$YELLOW
        terminator='$'
        ;;
esac

case "$HOSTNAME" in 
    hugin)          hostcolor=${BLUE} ;;
    wintermute)     hostcolor=$BOLD$WHITE;;
    dev1)           hostcolor=$BOLD$CYAN ;;
    # munin)          hostcolor=$RED ;;
    munin)          hostcolor=$BOLD$WHITE ;;
    xathan)         hostcolor=$MAGENTA ;;
    dathan)         hostcolor=${BOLD}${YELLOW} ;;
    hapax)          hostcolor=${BOLD}${WHITE} ;;
    gir)            ;;
    prod-app01.bits.illinoisstate.edu)   hostcolor=$BOLD$CYAN ;;
    prod-app02.bits.illinoisstate.edu)   hostcolor=$BOLD$CYAN ;;
    *)              hostcolor=$GREEN ;;
esac

# enable fancy git prompt if possible
if ! type __git_ps1 &> /dev/null && [ -e /usr/share/git-core/contrib/completion/git-prompt.sh ]; then
        . /usr/share/git-core/contrib/completion/git-prompt.sh
fi
if [ "$(type -t __git_ps1)" == "function" ]; then
    # enable extra git info
    GIT_PS1_SHOWDIRTYSTATE=1        #... untagged(*) and staged(+) changes
    GIT_PS1_SHOWSTASHSTATE=1        #... stashed($) changes
    GIT_PS1_SHOWUNTRACKEDFILES=1    #... untracked files(%)
    GIT_PS1_SHOWUPSTREAM=1          # trying this out too
    GIT_PS1_SHOWCOLORHINTS=1        # not sure what this does
    gitsection="\[$BOLD$RED\]\$(__git_ps1 '(%s)')"
else
    gitsection=""
fi


# identify chroot if we're in one, to prefix the prompt below
if [ -z "$debian_chroot" ] && [ -r /etc/debian_chroot ]; then
    debian_chroot=$(cat /etc/debian_chroot)
fi

function build_prompt() {
    local p="${debian_chroot:+($debian_chroot)}"
    p="$p\[$usercolor\]\u"
    p="$p\[$RESET$YELLOW\]@"
    p="$p\[$hostcolor\]\h"
    p="$p\[$RESET\]:"
    p=$p$(colorize_path_segments "`pwd`")
    p="$p$gitsection"
    p="$p\[$RESET\]$terminator "

    echo "$p"
}

case "$TERM" in
    # support non-color fallback for unknown terminals
    # TODO: find more reliable method of detecting color capability
    # maybe $(tput colors)...  does cygwin have tput?
    konsole|konsole-256color|xterm-color|xterm-256color|xterm|cygwin|linux|screen|screen-256color) 
        export PROMPT_COMMAND='PS1="$(build_prompt)"'
        ;;
    *) 
        PS1='${prefix}\u@\h:\w\$ '
        ;;
esac

# TODO consider refactoring for more sanitary scoping
# right now this thing creates a lot of variables it just leaves around.
# either recalculate every time and use function-local variables,
# or perhaps prefix all the variables with something unlikely to collide.