Only allow students to access sessions in progress with the read only flag, teachers can create tmux sessions as they wish.

tmux-teacher.sh

#!/bin/bash
#
# ~/.tools/tmux-teacher.sh
#
# Author: Daniel H. Hemmingsen <dhh@v5.dk>
# Usage: tmux-teacher.sh session-name /path/to/start/from"
#

TEACHER_GROUP="teacher"

create_session() {
	# Create and detach from new session
	tmux new-session -s $1 -d

	# Rename main window to the same as the session
	tmux rename-window $1 -t $1

	# Split the window horizontally 50/50.
	# The focus will be in the right pane.
	tmux split-window -h -t $1

	# Split the right pane 50/50.
	# The bottom right pane will now be in focus.
	tmux split-window -v -t $1

	# If path is given, start all panes in given path
	if [[ $2 ]]; then
		tmux send-keys -t $1:0.0 'cd '$2'; clear' C-m
		tmux send-keys -t $1:0.1 'cd '$2'; clear' C-m
		tmux send-keys -t $1:0.2 'cd '$2'; clear' C-m
	fi

	# Focus the first pane
	tmux select-pane -t $1:.+

	# Attach to new session
	tmux attach -t $1
}

# Main script

if [[ $1 ]]; then
	# Check if there is already a session with the given name
	if tmux has-session -t $1; then
		if groups $(whoami) | grep -qw "$TEACHER_GROUP"; then
			# Attach to session as teacher (write and read)
			tmux attach -t $1 && exit 0
		else
			# Attach to session as a student (read-only)
			tmux attach -r -t $1 && exit 0
		fi
	fi

	# No session was found, so let's make one if we are a teacher
	if groups $(whoami) | grep -qw "$TEACHER_GROUP"; then
		# Create sesssion and attach to it
		create_session $1 $2
		exit 0
	else
		echo "You need to be a teacher to create a tmux session"
		exit 1
	fi
fi