@BeastyBlacksmith This didn't seem to work for you on Linux: where/how did you install it? Is the math executable in your path?

Mathematica is installed by the IT department on a network drive. Both math and mathematica are on the path by default.

Nice, so we should be able to use that to find the correct path.

@BeastyBlacksmith Can you check if the following gives the correct paths?

archdir = Sys.ARCH == :arm ?    "Linux-ARM" :
          Sys.ARCH == :x86_64 ? "Linux-x86-64" :
                                "Linux"
basepath = String(read(pipeline(`math -noprompt`, stdin=IOBuffer("WriteString[\$Output,\$InstallationDirectory]"))))

lib = Libdl.find_library(
    ["libML$(Sys.WORD_SIZE)i4","libML$(Sys.WORD_SIZE)i3"],
    [joinpath(basepath,"SystemFiles/Links/MathLink/DeveloperKit",archdir,"CompilerAdditions")])
ker = joinpath(basepath,"Executables/MathKernel")

this works on my machine

I have improved the Linux handling in #27. I would still like to improve the handling on Windows: if anyone wants to help out, I would appreciate if you could install Mathematica or Wolfram Engine, then look in the Windows registry to find the entries which give the installation path.