title: tmux + fish shell; conf being sourced twice
body: <p>When I start <code>tmux</code>, my <code>~/.config/fish/config.fish</code> seems to be sourced <em>again</em>. This means any <code>set PATH foo $PATH</code> statements in my <code>config</code> get executed again, which leads to my PATH variable having duplicate entries in it. This isn't drastic, but it is annoying to ECHO path. when it is so long </p>
  
  <p>How can I prevent this problem? </p>
  
  <p>EDIT: the only fish related entires in my tmux file are </p>
  
  <p><code>
   #fix vim
   set -g default-shell $SHELL
   set -g default-command "reattach-to-user-namespace -l ${SHELL}"
   set -g default-command 'reattach-to-user-namespace $SHELL --login'
  </code></p>