My bash prompt settings

.bashrc

####
# Bash prompt w/ runtime of last series of commands (e.g. sleep 1 && sleep 1 correctly represented as 2s)
####
smiley () {
  printf :\\"$(($??50:51))";
}
print_elapsed () {
  NOW=`date +%s%N`
  DIFF=$(expr $NOW - $PT_LAST_TIME)
  DIV=1
  SUFFIX="ns"
  DIFFLEN=$(expr length $DIFF)
  if [[ $DIFFLEN -gt 10 ]]; then
    DIV=1000000000
    SUFFIX="s"
  elif [[ $DIFFLEN -gt 7 ]]; then
    DIV=1000000
    SUFFIX="m"
  elif [[ $DIFFLEN -gt 4 ]]; then
    DIV=1000
    SUFFIX="u"
  fi
  # expr prints a warning when result is float, so...
  DIFF=$(echo "$DIFF $DIV" | awk '{ print $1 / $2 - ($1 / $2 % 1); }')
  printf %4d $DIFF
  echo -e $SUFFIX
}
print_path () {
  pwd | awk '{print substr($0, length($0) - 59)}'
  # Update our command number....
  echo `expr \`cat $PT_CMD_FILE 2>/dev/null\` + 1` > $PT_CMD_FILE
}
maybeUpdate () {
  VAL=$1
  if [ "$2" != "$3" ]; then
    VAL=`date +%s%N`
    # echo -e "SET: \n  $2\n  $3" 1>&2
  fi
  printf $VAL
}
export PT_DIR=/run/shm/prompt
mkdir -p $PT_DIR
export PT_CMD_FILE="$PT_DIR/prompt-cmd-no-$$"
export PT_LAST_TIME=`date +%s%N`
export PT_CMD_LAST=0
trap 'rm -f $PT_CMD_FILE' EXIT
trap 'PT_LAST_TIME=`maybeUpdate $PT_LAST_TIME $PT_CMD_LAST "\`cat $PT_CMD_FILE 2>/dev/null\`"` PT_CMD_LAST=`cat $PT_CMD_FILE 2>/dev/null`' DEBUG
export PS1="\h\$(smiley)\$(print_elapsed) \e[30;1m\$(print_path)\e[0m\n\$ "