Syntax to get the value of environment variable in Kconfig file

Question

Can anyone provide me the syntax of obtaining the value of environment variable in Kconfig file?

Based on the value of environment variable I need to conditionally source another Kconfig file.

Answer 1

You will need to capture the value of the environment variable in a config symbol using 'option env', like in the following:

config ENV_VAR
    string
    option env="ENV_VAR"

if ENV_VAR = "foo"
source "foo_file"
endif

As a side note, $-references in 'source' statements refer to config variables, not to environment variables. You can't do something like

source "foo/$ENV_VAR/Kconfig"

You will instead need to do

config ENV_VAR_SYM
    string
    option env="ENV_VAR"

source "foo/$ENV_VAR_SYM/Kconfig"

(ENV_VAR_SYM could of course be called ENV_VAR as well; I just changed the name to clarify things.)

For another example, see the top-level Kconfig file in the kernel root.

(I'm the author of Kconfiglib Kconfiglib, a library for working with Kconfig-based configuration systems.)

Answer 2

As per the kconfig docs:

<expr> ::= <symbol>                             (1)
           <symbol> '=' <symbol>                (2)
           <symbol> '!=' <symbol>               (3)
           '(' <expr> ')'                       (4)
           '!' <expr>                           (5)
           <expr> '&&' <expr>                   (6)
           <expr> '||' <expr>                   (7)


- misc options: "option" <symbol>[=<value>]

  - "env"=<value>
  This imports the environment variable into Kconfig.

if:

    "if" <expr>
    <if block>
    "endif"

This defines an if block. The dependency expression <expr> is appended
to all enclosed menu entries.

source:

    "source" <prompt>

This reads the specified configuration file. This file is always parsed.

So I'd try

option env="YOURVAR"
if YOURVAR=foo
    source "somefile"
endif
if YOURVAR!=foo
    source "someotherfile"
endif