A quick attempt to automate opening up a tmux session with Irssi and its nicklist.pl running.

tmux_irssi_niclist.sh

#!/usr/bin/env bash
# This should work whether you are already in a TMUX session or not...
# Irssi directory is assumed to be in the user's home dir
if [ -z "$TMUX" ]
then
    tmux new-session -d -s ircuser 
    tmux split-window -tircuser -h -l20
    tmux send-keys -tircuser "tmux send-keys -t0 \"irssi\" C-m; \ 
        tmux send-keys -t0 \"/set nicklist_height \$(stty size | cut -f1 -d' ' -)\" C-m; \
        tmux send-keys -t0 \"/set nicklist_width \$(stty size | cut -f2 -d' ' -)\" C-m; \ 
        tmux send-keys -t1 \"cat ~/.irssi/nicklistfifo\" C-m; \
        tmux send-keys -t0 \"/nicklist fifo\" C-m; \
        tmux select-pane -t0" C-m
    tmux attach-session -t ircuser
else
    tmux split-window -h -l20
    tmux send-keys -t1 "tmux send-keys -t0 \"irssi\" C-m; \
        tmux send-keys -t0 \"/set nicklist_height \$(stty size | cut -f1 -d' ' -)\" C-m; \
        tmux send-keys -t0 \"/set nicklist_width \$(stty size | cut -f2 -d' ' -)\" C-m; \
        tmux send-keys -t0 \"/nicklist fifo\" C-m; \
        cat ~/.irssi/nicklistfifo" C-m
fi

@megalithic I talked to elithrar over email about this already a while ago... this script is something I whipped up to get it working for my personal needs, but you may need to tweak it to work for your purposes. I think the problem he was having was that he was running it from inside a tmux session, which this isn't designed to handle. I can't remember exactly what solution we came up with, but I think it looked something like...

!/bin/bash

if [ -z "$IRSSI_PATH" ]
then
echo "Environment variable IRSSI_PATH not set."
exit
fi

tmux split-window -h -l 20
tmux send-keys -t0 "irssi" C-m
tmux send-keys -t0 "/set nicklist_height $(stty size | cut -f1 -d' ' -)" C-m
tmux send-keys -t0 "/set nicklist_width $(stty size | cut -f2 -d' ' -)" C-m
tmux send-keys -t0 "/nicklist fifo" C-m
cat $IRSSI_PATH/nicklistfifo

UPDATE: it seems like there's a lot of confusion about this, so I updated it to automatically detect if it's in a TMUX session and act accordingly.