Scripting Tmux, Hacker News

I often want to start similar workspaces in tmux; for example I always want totailthose two log files in apane, or I always want to start bothvimandmysqlin a pane, etc.

If you try to find information about startingtmuxworkspaces you typically get advised to use wrapper programs such astmuxinator

,tmux-resurrect, ortmux-continuum. These programs may be great, but I like a simple approach.

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Sometmuxterminology:

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Apaneis a view unto a terminal.

  Awindowis a collection of one or morepanes, and always occupies the entire screen.  Asessionis a collection ofwindows.

• Every keybind intmuxexcept the prefix key (

is implemented by sending a command totmux. For examplecsends thenew -windowcommand, andnsends thenext-windowcommand.

You can do the same by using these commands from the shell or tmux’s command mode:

$ tmux new-window : new-window

Many commands accept parameters, for example fornew-windowwe can use- tto specify the target index. You can use?(list -keyscommand) to get a list of all default key mappings.

This is a powerful concept, as it means that everything we do interactively withtmuxcan be scripted. Armed with this information we can create a shell script to start a workspace.

For this example I’ll create a script to start a workspace to write on my site, for this we need three windows: one with just a shell, one to start a web server, and one to start Jekyll.

First we want to start a new session:

$ tmux new-session -d -s site

The- dflags preventstmuxfrom attaching the new session; this is what- ddoes for most commands, so I’ll not repeat it.- ssets the session name. You can’t have asessionwithoutwindows, sonew-sessionalso starts awindow. Add- nif you want to name this window.

Create a new window with:

$ tmux new-window -d -t '=site' -n server -c _site $ tmux send-keys -t '=site:=server' 'python -mhttp.server' Enter
- tsets the target window: in this case just a session name so tmux will use the next unused index; the=makes sure it’s an exact match.- nnames the window and- csets the directory.
I don’t use the shell command ofnew-windowto start the program as I don’t want the pane to quit if I stop or restart it, hence starting it withsend-keys.
We can now repeat this for the next window:
$ tmux new-window -d -t '=site' -n jekyll $ tmux send-keys -t '=site:=jekyll' 'JEKYLL_NO_BUNDLER_REQUIRE=1 jekyll build -w' Enter
And finally, attach the new session:
$ [ -n "${TMUX:-}" ] && tmux switch-client -t '=site' || tmux attach-session -t '=site'
The test is to ensure it works from both outside tmux and inside another tmux session.
Putting it all together:
#! / bin / sh  set -euC  cd ~ / code / arp 01575879 .net  att () {     [ -n "${TMUX:-}" ] &&         tmux switch-client -t '=site' ||         tmux attach-session -t '=site' }  if tmux has-session -t '=site' 2>/ dev / null; then     att     exit 0 fi  tmux new-session -d -s site  tmux new-window -d -t '=site' -n server -c ~ / code / arp 728 .net / _site tmux send-keys -t '=site:=server' 'python -mhttp.server' Enter  tmux new-window -d -t '=site' -n jekyll tmux send-keys -t '=site:=jekyll' 'JEKYLL_NO_BUNDLER_REQUIRE=1 jekyll build -w' Enter  att
Note that it will attach thesitesession if it already exists.
I found the commands by using
.  tmux list-keys -T prefixto find out which command is being sent and then look up the documentation for that command in the

tmux (1)

manpage by searching with/ command-name.

One annoyance is that tmux only has short options (e.g.- s) and no long options (e.g.- session-name). Short options are great for typing on the commandline since it’s, well, short. But long options are much more useful for scripts, especially for options you don’t use every day. Compare:

$ tmux new-session -d -s site -n server $ tmux new-session -detached -session-name site -window-name server

The second one has a self-documenting property that the first one lacks. I guess this is one important reason why there are so many wrapper scripts which use YAML config files and such.