How to use variable in backticks?

[Boscop]

How can I do this?

foo := `echo {{bar}} | tr '[:upper:]' '[:lower:]'`

Or this:

version := `sed -En 's/version[[:space:]]*=[[:space:]]*"([^"]+)"/v\1/p' {{foo}}/Cargo.toml | head -1`

When I do this, they are not substituted.

[casey]

This isn't currently supported, but there's an open issue for it: #11

The design I currently favor, to avoid breaking backwards compatibility, is to require strings and backticks inside of which interpolation is desired to be proceeded by a f, so:

foo := f`echo {{bar}} | tr '[:upper:]' '[:lower:]'`