Start emacsclient and only create a new frame if none exists. Otherwise reuse frame. Pass -nw to force console-emacs

e.sh

#!/bin/bash -e

if [[ "$DISPLAY" ]]; then
        frame=`emacsclient -a '' -e "(member \"$DISPLAY\" (mapcar 'terminal-name (frames-on-display-list)))" 2>/dev/null`
        [[ "$frame" == "nil" ]] && opts='-c' # if there is no frame open create one
        [[ "${@/#-nw/}" == "$@" ]] && opts="$opts -n" # don't wait unless we've asked to run in a terminal
else
        opts='-nw'
fi

exec emacsclient -a '' $opts "$@"

Source and copyright: https://emacs.stackexchange.com/questions/12894/make-emacsclient-create-a-frame-only-if-there-isnt-one-already