No subject

properties expansion is MP_CMD_OSD_SHOW_PROPERTY_TEXT
(osd_show_property_text)

You can do something like:
INS osd_show_property_text "${path}"

and internally, it calls m_properties_expand_string() to turn the
${path} into something useful.

It doesn't look like MP_CMD_RUN (run) does anything similar.

You might be able to use the show_property example to modify run for
your local use (just to see if it works the way you want).

If it works well, you might submit a patch.  It seems to me like it
wouldn't need a separate command to have this type of feature... I
mean, really, how many people would do something like:

KEY run "echo ${PATH}"

to use an environment variable rather than a property?

Well, OK, maybe some folks do, and you'd really need a new command like:
run_with_property

mrc