How to modify files in post-build script depending on a menuconfig flag? - authentication

Question

I need to find a way to modify/edit a given file after Buildroot compilation and right before the creation of the rootfs depending on a menuconfig flag selection. I could find in the Buildroot documentation that it is possible to do that by using post-build scripts.
My problem is that I would do the script action only if I selected something in menuconfig, for example:
(x) Enable my_login_system;
If I select my_login_system, then I need to change the nsswitch.conf file according:
passwd: my_login files
If I don't select in menuconfig the "my_login_system", then the nsswitch.conf should be:
passwd: files my_login
So, my main question is how to know if the "my_login_system" was selected or not in the post-build script.

Answer 1

When a post-build scripts is executed, it can access the BR2_CONFIG environment variable, which holds the path to the Buildroot .config file. Your script can parse that file and act accordingly.
Thus you could have a condition like:
if grep -q ^BR2_MY_LOGIN_SYSTEM=y ${BR2_CONFIG}
then
# do some tweaks
else
# do other tweaks
fi
Alternatively, you could use the BR2_ROOTFS_POST_SCRIPT_ARGS configuration variable to pass arbitrary command line parameters (as opposed to environment variables) to the post-build scripts.
Both possibilities are documented in the Buildroot manual, at section Customizing the generated target filesystem.