$`command line` (with patched P4)
-Sub-shell call of ``command line`` and retrieves its stdout/err outputs
-by function ``func``. The string is replaced by an execution of the string
-by a function named ``command``. You need to provide this ``command`` function
-in the context. For example, you can use ``Spotlib.Spot.Unix.shell_command``.
+Sub-shell call of ``command line`` by `Spotlib.Spot.Unix.Command.shell_command`
+and retrieves its status and stdout outputs.
In P4 quotes, if you want to use shell appending redirect `>>`, you must escape it: