gistfile1.sh

# improved version of the code in Eivind Uggedal's comment at
# http://justinchouinard.com/blog/2010/04/10/fix-stale-ssh-environment-variables-in-gnu-screen-and-tmux/

function preexec() {
  if [[ -n $TMUX ]]; then
      TMUX_SOCK=$(echo $TMUX|cut -d , -f 1)
      NEW_SSH_AUTH_SOCK=$(tmux -S $TMUX_SOCK showenv|grep ^SSH_AUTH_SOCK|cut -d = -f 2)
      if [[ -n $NEW_SSH_AUTH_SOCK ]] && [[ -S $NEW_SSH_AUTH_SOCK ]]; then
          SSH_AUTH_SOCK=$NEW_SSH_AUTH_SOCK
      fi
  fi
}

Awesome! My psshes are so happy.

I like doing it elisp hook-style:

update_auth_sock () {
  if [[ -n $TMUX ]]; then
    TMUX_SOCK=$(echo $TMUX|cut -d , -f 1)
    NEW_SSH_AUTH_SOCK=$(tmux -S $TMUX_SOCK showenv|grep ^SSH_AUTH_SOCK|cut -d = -f 2)
    if [[ -n $NEW_SSH_AUTH_SOCK ]] && [[ -S $NEW_SSH_AUTH_SOCK ]]; then
      SSH_AUTH_SOCK=$NEW_SSH_AUTH_SOCK
    fi
  fi
}
preexec_functions+=update_auth_sock