Now it gets turned into '^[_[[:alpha:]]][_[[:alnum:]]]*$', which still doesn’t look right. Looks like the inner pair of brackets does not need to be escaped.

I think, you also could redirect the output of the if condition to /dev/null so that it doesn’t spam the terminal with variable names.

Also, I am getting

./configure: line 8551: 2.2: command not found

a number of times, which, I think, come from lines similar to this one in config.status:

S["PACKAGE_STRING"]="nix 2.2"

and missing quotes in the eval line.

There is also a number of lines of the form

./configure: line 8551: -lsodium: command not found

I’ve got another regression. It looks a lot like it was introduced by the same commit.

src/libstore/s3-binary-cache-store.cc:95:23: error: invalid token at start of a preprocessor expression
#if AWS_VERSION_MAJOR == 1 && AWS_VERSION_MINOR < 3

in config.status:

D["AWS_VERSION_MAJOR"]=" "
D["AWS_VERSION_MINOR"]=" "

I've reverted this and the previous commit for now.