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NAME

       win32reg - win32reg provides access to the registry on Windows

DESCRIPTION

       win32reg  provides  read  and  write  access  to the registry on Windows. It is essentially a port driver
       wrapped around the Win32 API calls for accessing the registry.

       The registry is a hierarchical database, used  to  store  various  system  and  software  information  in
       Windows.  It  is available in Windows 95 and Windows NT. It contains installation data, and is updated by
       installers and system programs. The Erlang installer updates the registry  by  adding  data  that  Erlang
       needs.

       The  registry  contains  keys  and  values.  Keys  are like the directories in a file system, they form a
       hierarchy. Values are like files, they have a name and a value, and also a type.

       Paths to keys are left to right, with sub-keys to the right and backslash between  keys.  (Remember  that
       backslashes  must  be  doubled  in  Erlang  strings.)  Case  is  preserved  but not significant. Example:
       "\\hkey_local_machine\\software\\Ericsson\\Erlang\\5.0" is the key for  the  installation  data  for  the
       latest Erlang release.

       There  are  six  entry  points  in  the  Windows registry, top level keys. They can be abbreviated in the
       win32reg module as:

       Abbrev.          Registry key
       =======          ============
       hkcr             HKEY_CLASSES_ROOT
       current_user     HKEY_CURRENT_USER
       hkcu             HKEY_CURRENT_USER
       local_machine    HKEY_LOCAL_MACHINE
       hklm             HKEY_LOCAL_MACHINE
       users            HKEY_USERS
       hku              HKEY_USERS
       current_config   HKEY_CURRENT_CONFIG
       hkcc             HKEY_CURRENT_CONFIG
       dyn_data         HKEY_DYN_DATA
       hkdd             HKEY_DYN_DATA

       The key above could be written as "\\hklm\\software\\ericsson\\erlang\\5.0".

       The win32reg module uses a current key. It works much like the current directory. From the  current  key,
       values can be fetched, sub-keys can be listed, and so on.

       Under a key, any number of named values can be stored. They have name, and types, and data.

       Currently, the win32reg module supports storing only the following types: REG_DWORD, which is an integer,
       REG_SZ which is a string and REG_BINARY which is a binary. Other types can be read, and will be  returned
       as binaries.

       There is also a "default" value, which has the empty string as name. It is read and written with the atom
       default instead of the name.

       Some  registry  values  are  stored  as  strings  with  references   to   environment   variables,   e.g.
       "%SystemRoot%Windows".  SystemRoot  is  an environment variable, and should be replaced with its value. A
       function expand/1 is provided, so that environment variables surrounded in % can  be  expanded  to  their
       values.

       For additional information on the Windows registry consult the Win32 Programmer's Reference.

DATA TYPES

       reg_handle()

              As returned by open/1.

       name() = string() | default

       value() = string() | integer() | binary()

EXPORTS

       change_key(RegHandle, Key) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 Key = string()
                 ReturnValue = ok | {error, ErrorId :: atom()}

              Changes the current key to another key. Works like cd. The key can be specified as a relative path
              or as an absolute path, starting with \.

       change_key_create(RegHandle, Key) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 Key = string()
                 ReturnValue = ok | {error, ErrorId :: atom()}

              Creates a key, or just changes to it, if it is already there. Works like a  combination  of  mkdir
              and cd. Calls the Win32 API function RegCreateKeyEx().

              The registry must have been opened in write-mode.

       close(RegHandle) -> ok

              Types:

                 RegHandle = reg_handle()

              Closes the registry. After that, the RegHandle cannot be used.

       current_key(RegHandle) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 ReturnValue = {ok, string()}

              Returns the path to the current key. This is the equivalent of pwd.

              Note  that the current key is stored in the driver, and might be invalid (e.g. if the key has been
              removed).

       delete_key(RegHandle) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 ReturnValue = ok | {error, ErrorId :: atom()}

              Deletes the current key, if it is valid. Calls the Win32 API function  RegDeleteKey().  Note  that
              this call does not change the current key, (unlike change_key_create/2.) This means that after the
              call, the current key is invalid.

       delete_value(RegHandle, Name) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 Name = name()
                 ReturnValue = ok | {error, ErrorId :: atom()}

              Deletes a named value on the current key. The atom default is used for the the default value.

              The registry must have been opened in write-mode.

       expand(String) -> ExpandedString

              Types:

                 String = ExpandedString = string()

              Expands a string containing environment variables between percent characters. Anything between two
              % is taken for a environment variable, and is replaced by the value. Two consecutive % is replaced
              by one %.

              A variable name that is not in the environment, will result in an error.

       format_error(ErrorId) -> ErrorString

              Types:

                 ErrorId = atom()
                 ErrorString = string()

              Convert an POSIX errorcode to a string (by calling erl_posix_msg:message).

       open(OpenModeList) -> ReturnValue

              Types:

                 OpenModeList = [OpenMode]
                 OpenMode = read | write
                 ReturnValue = {ok, RegHandle} | {error, ErrorId :: enotsup}
                 RegHandle = reg_handle()

              Opens the registry for reading or writing. The current key will be the  root  (HKEY_CLASSES_ROOT).
              The read flag in the mode list can be omitted.

              Use change_key/2 with an absolute path after open.

       set_value(RegHandle, Name, Value) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 Name = name()
                 Value = value()
                 ReturnValue = ok | {error, ErrorId :: atom()}

              Sets  the  named  (or  default)  value to value. Calls the Win32 API function RegSetValueEx(). The
              value can be of three types, and the corresponding registry type will be used. Currently the types
              supported are: REG_DWORD for integers, REG_SZ for strings and REG_BINARY for binaries. Other types
              cannot currently be added or changed.

              The registry must have been opened in write-mode.

       sub_keys(RegHandle) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 ReturnValue = {ok, [SubKey]} | {error, ErrorId :: atom()}
                 SubKey = string()

              Returns a list of subkeys to the current key. Calls the Win32 API function EnumRegKeysEx().

              Avoid calling this on the root keys, it can be slow.

       value(RegHandle, Name) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 Name = name()
                 ReturnValue = {ok, Value :: value()}
                             | {error, ErrorId :: atom()}

              Retrieves the named value (or default) on the current key. Registry values  of  type  REG_SZ,  are
              returned  as strings. Type REG_DWORD values are returned as integers. All other types are returned
              as binaries.

       values(RegHandle) -> ReturnValue

              Types:

                 RegHandle = reg_handle()
                 ReturnValue = {ok, [ValuePair]} | {error, ErrorId :: atom()}
                 ValuePair = {Name :: name(), Value :: value()}

              Retrieves a list of all values on the current key. The values  have  types  corresponding  to  the
              registry types, see value. Calls the Win32 API function EnumRegValuesEx().

SEE ALSO

       Win32 Programmer's Reference (from Microsoft)

       erl_posix_msg

       The Windows 95 Registry (book from O'Reilly)