How to create new tmux session if none exists

Question

I am trying to figure out how to attach to a tmux session if a named tmux session exists, if not I want to create a new one with the given name.

Currently, I know of a few tmux commands which can partly achieve what I am looking for, but its not clear how to combine them together to get what I am looking for:

• tmux attach attaches to an automatically existing session - but errors out if no session exists
• tmux new creates a new session - but it does so every time, so I can't leave it in my .tmux.conf
• tmux has-session tests whether a session exists - but I don't know how to stitch it together with the other commands

Thus, I would like to create a tmux script, so that this happens automatically, instead of having to manually create it everytime I need to log into a sessions.

How can I write a automatic script so as to create a new tmux session (if a given session name doesnt exist) or attach to a session name (if it exists)?

Answer 1

I figured it out (and had it pointed out to me).

tmux attach || tmux new

Answer 2

Alternately, you can add

new-session

to your .tmux.conf - that will create a default session on server start.

Then tmux attach will either attach to the current session (running server, that is), or create a new session (start the server, read the config file, issue the new-session command) and attach to that.

Answer 3

As pointed out in comments from Petr Viktorin, jkoelker and pjincz, you can use the following command to attach to mySession if it exists, and to create it if it doesn't:

 tmux new -A -s mySession

From man tmux:

new-session[-AdDEP] [-cstart-directory] [-Fformat] [-nwindow-name] [-ssession-name] [-tgroup-name] [-xwidth] [-yheight] [shell-command]

(alias: new)

Create a new session with name session-name.

[...]

The -A flag makes new-session behave like attach-session if session-name already exists; in this case, -D behaves like -d to attach-session.

new-session has supported -A since tmux-1.8.

Answer 4

Adapting Alex's suggestion to include project based configuration upon startup, I started using the following:

# ~/bin/tmux-myproject shell script
# The Project name is also used as a session name (usually shorter)
PROJECT_NAME="myproject"
PROJECT_DIR="~/myproject"

tmux has-session -t $PROJECT_NAME 2>/dev/null
if [ "$?" -eq 1 ] ; then
    echo "No Session found.  Creating and configuring."
    pushd $PROJECT_DIR
    tmux new-session -d -s $PROJECT_NAME
    tmux source-file ~/bin/tmux-${PROJECT_NAME}.conf
    popd
else
    echo "Session found.  Connecting."
fi
tmux attach-session -t $PROJECT_NAME

where tmux-myproject.conf is my startup series of tmux commands to create my windows and panes, as well as start my editors.

Answer 5

Although I find rampion's answer is sufficient for using 1 session, this script lets you setup multiple sessions:

SESSIONS="work play"

function has-session {
    tmux has-session -t $1 2>/dev/null
}

function except 
{
    if [ "$?" -eq 1 ] ; then
        $1
    fi
}

# Configure your sessions here
function session-work
{
    tmux new-session -d -s work
    tmux neww -k -t work:1
}

function session-play
{
    tmux new-session -d -s play
    tmux neww -k -t play:1
}

#
#MAIN 
for x in $SESSIONS
do
    echo $x
    has-session $x
    except session-$x
done

NOTE:

-k  --> new-window will not be created if already exists
-d  --> start session or window, but don't attach to it yet
-s  --> name the session
-t  --> specify a target location in the form session:window.pane 

Answer 6

I use an alias to create a new session if needed, and attach to my default session if it already exists:

alias tmuxre='tmux new-session -t default || tmux new-session -s default'

I added this to my .login on my server.

The reason I do it this way is because I don't want to attach to the same actual session, I want a new session which uses the same group of windows.

This is also similar to running screen -xRR.

Answer 7

For those who want to do the same thing in fish:

tmux attach -t mysesh; or tmux new -s mysesh