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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)