Abbreviating PROMPT_COMMAND with ${HOME} to ~ replacement using perl

gistfile1.sh

#!/bin/bash
PROMPT_COMMAND='PS1X=$(perl -p -e "s|^${HOME}|~|;s|([^/])[^/]*/|$""1/|g" <<<${PWD})'
PS1='\j \u@\h:${PS1X}  '
# http://unix.stackexchange.com/a/26860/6128