tmux equivalent of “screen -R”?

Question

The tmux attach command acts more like a combination of screen -r and screen -x -- first it trys to attach to the most recently detached session, and then if none is available it will attach to a currently attached session. I want to emulate the behavior of screen -R: first try to attach to a detached session, then start a new session if there were no detached sessions. What is the best way to achieve this in tmux?

Answer 1

After consulting the wizards of IRC I am confident there is no single tmux command that has this behavior. Luckily, it is fairly easy to emulate using the shell:

(tmux ls | grep -vq attached && tmux at) || tmux

Answer 2

Despite what it says in tmux manual:

             The target-session rules for attach-session are slightly
         adjusted: if tmux needs to select the most recently used session,
         it will prefer the most recently used unattached session.

Drew's answer won't work properly in a situation like:

0: 1 windows (created Wed Nov  7 23:51:08 2012) [177x47]
1: 1 windows (created Wed Nov  7 23:51:33 2012) [177x47] (attached)

tmux at will attach to the last session (#1) (even though this session is still attached somewhere else). This ruins the whole idea of running several tmux sessions and attaching only to a detached one (to use mosh + tmux + iterm2 to create a perfect roaming terminal).

Another approach would be to manually select a non-attached session:

tmux ls | grep -vq attached && tmux at `tmux ls | grep -vm1 attached | cut -d: -f1`

Answer 3

I tend to only have two tmux sessions at a time, so I do something like this in each terminal window.

terminal window 0:

tmux attach -t 0 || tmux new

terminal window 1:

tmux attach -t 1 || tmux new

Answer 4

This has worked the best for me:

if [ -z "$TMUX" ]; then
     (tmux ls | grep -vq attached && tmux at -t `tmux ls | grep -vm1 attached | cut -d: -f1`) || tmux new
fi

The -t is needed to attach to the proper session.

Answer 5

What about

tmux attach || tmux new

or instead just create the file ~/.tmux.conf if it doesn't exist, and add

new-session

to it such that it creates a new session when there is none when you run tmux attach.

It might also be handy to make tmux an alias to tmux attach.