How To Use Erlang Win32Reg to Read Windows Registry Keys?

Question

I'm tagging this as both Erlang and Elixir because my sample code is in Elixir but I suspect the answer will involve the Erlang Win32Reg library.

Windows 8.1 x64

Erlang 17.4

Elixir 1.0.3

I do the following from Iex on Windows:

{:ok, handle} = :win32reg.open([:read])
:ok = :win32reg.change_key(handle, :local_machine)

When I do this I get this error:

** (FunctionClauseError) no function clause matching in :win32reg.split_key/3
    (stdlib) win32reg.erl:364: :win32reg.split_key(:local_machine, [], [])
    (stdlib) win32reg.erl:340: :win32reg.parse_relative/2
    (stdlib) win32reg.erl:122: :win32reg.change_key/3

However if I use this code instead:

:ok = win32reg.change_key(handle,'HKEY_LOCAL_MACHINE')

It works as expected. I tried this same code directly in the werl shell and the result is the same.

1.) Shouldn't :local_machine work the same?

2.) When I change to the HKLM key and do this:

{:ok, sub_keys} = :win32reg.sub_keys(handle)

I get this:

{:ok, ['Software']}

Going by what I see in regedit, there are several other subkeys below the HKLM key. Why aren't they showing up?

I can't easily test this on other versions of Windows so this issue may be specific to Windows 8.x. If that's the case, that's fine; I'm just trying to insure I'm not coding something incorrectly.

Leaf Garland Leaf Garland · Accepted Answer · 2015-03-26T11:41:43

Looking at the win32reg docs, the aliases you mention are valid but they are strings, as you can use them as elements of a path.

:win32reg.change_key(handle, '\\local_machine\\')

I've also found that you need to give it absolute paths initially, note the slash at the start.

With those changes I was able to see the same nodes as regedit.

How To Use Erlang Win32Reg to Read Windows Registry Keys?

1 Answers