My PS1

PS1.sh

# Thanks to @kroogs for the idea of making the text red on errors :D

# This is a global reference to be used in order to know the last return
# code from within functions.
last_response_code=$?

# Formats the provided text into something a bit more striking.
error_text () { echo "\033[31m${@}\033[0m"; }

# Generates our PS1 when passed the last program's response code, and
# whatever text we want in the PS1.
make_PS1 () {
  PS1_git=$(__git_ps1 "(%s) ")

  if [ ${last_response_code} = 0 ]; then
    echo "${PS1_git}${@} ";
  else
    echo -e "${PS1_git}`error_text ${@}` ";
  fi
}

# A PS1.
export PS1='`last_response_code=$?;make_PS1 \W`'