Run tmux command if current window is not zoomed using %if

Question

According to tmux man page, it is possible to use %if to conditionally run its commands. So I am trying to use it to zoom the current pane if it is not already zoomed (otherwise it would un-zoom it).

I tried some variations of

%if '#{window_zoomed_flag}' resize-pane -Z %endif

without success. Any ideas?

I've seem some examples to achieve what I am trying to do using if-shell, but I'd like to do it only with 'native' tmux commands. By 'native' I mean not spawning another process.

Answer 1

I've seem some examples to achieve what I am trying to do using if-shell, but I'd like to do it only with 'native' tmux commands. By 'native' I mean not spawning another process.

if-shell may or may not spawn a shell. See the description:

if-shell [-bF] [-t target-pane] shell-command command [command]

(alias: if)

Execute the first command if shell-command returns success or the second command otherwise. Before being executed, shell-command is expanded using the rules specified in the FORMATS section, including those relevant to target-pane. With -b, shell-command is run in the background.

If -F is given, shell-command is not executed but considered success if neither empty nor zero (after formats are expanded).

^(source)

Any command denoted command is a tmux command, it doesn't need a shell. shell-command needs a shell unless -F is given. Not every test can be performed with -F but in your case it's easy. This will not spawn another process:

tmux if-shell -F '#{window_zoomed_flag}' '' 'resize-pane -Z'

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To confirm that if-shell -F spawns no additional processes, do the following:

1. Work inside tmux, so tmux server exists. You will need two panes; create them beforehand.

2. Store the PID of the tmux server:

   pid="$(pgrep 'tmux: server')"
   

3. Verify the variable is not empty, just in case:

   echo "$pid"
   

4. Use strace to tell if the server creates new processes (see this answer):

   strace -e fork,vfork,clone,execve -fb execve -p "$pid"
   

5. Select the other pane and invoke:

   tmux if-shell -F '#{window_zoomed_flag}' '' 'resize-pane -Z'
   # now similar command to unzoom
   tmux if-shell -F '#{window_zoomed_flag}' 'resize-pane -Z'
   

6. Observe what strace printed. There should be no output.* This means no additional process was spawned.

7. For comparison, these are equivalent commands without -F, they do spawn shells:

   tmux if-shell '[ #{window_zoomed_flag} -eq 1 ]' '' 'resize-pane -Z'
   # now similar command to unzoom
   tmux if-shell '[ #{window_zoomed_flag} -eq 1 ]' 'resize-pane -Z'
   

   Each command will make execve("/bin/sh", … appear in the output from strace.

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^{* Unless you use a hook triggered by a pane being zoomed or resized, and the hook spawns another process. Temporarily remove the hook so it doesn't interfere with the test.}