Make emacsclient create a frame only if there isn't one already

Question

How can I make emacsclient -a '' -n create a new frame only if there isn't one already?

The problem with the -c flag is that it creates a new frame every time. The problem without it is that if there is no frame open it will open in the command line.

If I can check if there is an open Emacs frame from the shell, I can call with or without -c depending on that to get the behavior I want. I tried:

$ emacsclient -a '' --eval '(frames-on-display-list)'
(#<frame F1 0xba2740>)

I always get the same result.

I could use temporary files or pgrep, but those approaches are very error prone.

This is similar to this question, but it is not a duplicate, since the OP there was satisfied with having to have a frame open before calling emacsclient.

Answer 1

I ended up making this script based on this

#!/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 '' $opts "$@"

If there is no display it opens with -nw. If $DISPLAY is set it looks for frames in that display to see if it needs to make a new one.

Edit: I've modified it so that you can manually specify -nw if you want to open in a terminal even if there is a display.

Answer 2

You can use:

emacsclient -s server_name -e '(+ 1 0)' >/dev/null 2>&1

to check if the Emacs server "server_name" is already running. If the command returns exit code 0, it is running. If so, just use the emacsclient command:

emacsclient -s server_name -n file_name.txt

If it is not running, you can open a new Emacs server with for example:

emacs --eval '(setq server-name "server_name")' --eval '(server-start)' file_name.txt &