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optionally run several commands when starting tmux


I have a ~/.tmux/dev file which looks like this:


selectp -t 0    # select the first pane
splitw -h -p 50 # split it into two halves

selectp -t 1    # select the new, second (1) pane
splitw -v -p 50 # split it into two halves

selectp -t 0    # go back to the first pane
send-keys 'vim .' Enter

If I run tmux source-file ~/.tmux/dev from inside a tmux session, it works fine.


I want to create a bash script that opens tmux and automatically runs those commands.


I tried running


tmux new 'tmux source-file ~/.tmux/dev'

but I only see two panes; the pane with vim is missing.


I have read How do I get tmux to open up a set of panes without manually entering them?, but before installing a tool for managing tmux configs, I would like to grok what's happening here.


Thanks in advance for any light you can shed on the subject.



Answer



This is what is happening:




  1. tmux new 'tmux source-file ~/.tmux/dev'


    The new commands creates a new session with a single window that has a single pane. The command tmux source-file ~/.tmux/dev runs in this new pane.



    • So, you have a new session N (where N is some number), with

    • a single window N:0 (or whatever you have base-index set to), with

    • a single pane N:0.0 (or whatever you have base-pane-index set to),

    • running the command tmux source-file ~/.tmux/dev.




  2. The source-file command is processed.



    1. The extra panes are added.

    2. Pane 0 is (re)selected.

    3. The send-keys command then “types” vim . + Enter at pane 0.
      This input is ignored because this pane is just running the tmux client that sent the source-file command.



  3. The tmux client exits, thus closing pane 0.


So the unexpected bit is that pane 0 (i.e. N:0.0) is running (only) the source-file command which ignores your “typed” command. This pane never runs an interactive shell that could interpret the “typed” command.


There are at least a couple of ways you can fix this:




  • Start ~/.tmux/dev with new-window so that pane 0 is running your “default command” (i.e. probably an interactive shell).


    This method has the benefit of not assuming that your current pane is running an interactive shell, and also not assuming that the current pane is 0 (i.e. what happens if you run your original series of commands against a pane that is part of an already split window?). It means you can safely bind source-file ~/.tmux/dev to a key that you can run in any context (since it creates a new window for all of its panes). From the shell you can run either tmux source-file ~/.tmux/dev (to create a new window in the current session), or your original tmux new 'tmux source-file ~/.tmux/dev' to create a new session.


    A minor drawback to this method is that when you run tmux new 'tmux source-file ~/.tmux/dev', the initial window will still run the client that sends source-file and exit fairly quickly. This means that your “main window” (the one with the splits) will be one higher than your base-index and a future new window will be placed before the “main window”. You could fix this by using something like this:


    tmux new 'tmux move-window -t 99 \; source-file ~/.tmux/dev'

    It moves the (ephemeral) initial window to a high index so that the new-window in ~/.tmux/dev will end up at base-index.




  • Use (e.g.) tmux new 'tmux source-file ~/.tmux/dev ; zsh -l' so that the pane ends up running an interactive shell after the source-file command finishes.


    The ugly bit about this is that you end up “hard coding” your preferred shell into this command. Also, the send-keys input (vim . + Enter) is technically sent before the shell starts; this is probably okay, but may not always be completely reliable.


    You could avoid “hard coding” your shell by querying tmux for the default-command (or if that is not set, default-shell (or if that is not set, using SHELL)), but that may be more work than you really want to do.




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