tmuxでセッションの有無を判別して起動するスクリプト ref: http://qiita.com/d6rkaiz/items/993ef586aa39f2ddb588

file0.txt

#!/bin/bash

tmux ls > /dev/null
if [ $? -eq 1 -a -z "$TMUX" ]; then
    exec tmux
elif [ -z "$TMUX" ] ; then
    exec tmux attach
else
    echo "sessions should be nested with care."
fi