Setting env variable if not already set

[mmstick]

With Make:

prefix ?= /usr/local

Defines that prefix will only be assigned to /usr/local if it has not already been defined.

There doesn't seem to be a way to achieve this here in a reasonable way

[sagiegurari]

that's a good idea. I think adding the 'condition' structure to env definition will resolve it and also give you a lot more choices.
so you could do

[env]
prefix = { value = "/usr/local", condition = { env_not_set = [ "prefix" ] } }

and naturally in condition you will have access to all condition capabilities like env value checking, file exists and so on...

[sagiegurari]

@mmstick just pushed a change to the 0.24.3 development branch with condition support.
basically it looks like:

PREFER_EXISTING = { value = "new", condition = { env_not_set = ["PREFER_EXISTING"] } }
OVERWRITE_EXISTING = { value = "new", condition = { env_set = ["OVERWRITE_EXISTING"] } }

you can see the docs and example toml file.

[sagiegurari]

This is now published in the new cargo-make version.