Environment variables inside layout command arguments

[lockbox]

Similar to #2288 / #2291, except with environment variables inside the arguments in a layout

tangentially related to #2574, but focusing on
arguments to pane commands.

eg.

layout {
  pane command "watch" {
    args "$WATCH_COMMAND"
  }
}

TLDR; being able to expand env variables allows a lot more flexibility wrt sharing layout/config files with teammates etc.

I could probably devote some time to knock out a pr in a couple weeks, but I'm a little busy atm.

[brandondrew]

This would be extremely useful. My use case is to open panes that display information about remote servers, such as

pane name="production status" size="60%" command="ssh" { args "-t" "${PROJECT_SLUG}-prod" "htop"; }

I'm trying to create a layout that can be used across a dozen or so projects. The expansion of environment variables would be a convenient way to avoid a huge amount of duplication.