An example of a bash prompt showing RVM Ruby version and active gemset

rvm-prompt.sh

       RED="\[\033[01;31m\]"
     GREEN="\[\033[01;32m\]"
COLOR_NONE="\[\033[0m\]"

function ruby_version {
    if [[ -f ~/.rvm/bin/rvm-prompt ]]; then
        local system=$(~/.rvm/bin/rvm-prompt s)
        local interp=$(~/.rvm/bin/rvm-prompt i)
        if [[ ! -n $system ]]; then
            # Don't show interpreter if it's just MRI
            case $interp in
                ruby) echo " ${RED}♦ $(~/.rvm/bin/rvm-prompt v g)${COLOR_NONE}" ;;
                *)    echo " ${RED}♦ $(~/.rvm/bin/rvm-prompt i v g)${COLOR_NONE}" ;;
            esac
        fi
    fi
}

function prompt_func {
    previous_return_value=$?;
    prompt="${GREEN}\w${COLOR_NONE}$(ruby_version)\n[\u@\h]"
    if test $previous_return_value -eq 0
    then
        PS1="\n${prompt}\$ "
    else
        PS1="\n${prompt}${RED}\$${COLOR_NONE} "
    fi
}

export PROMPT_COMMAND=prompt_func