Provides access to the registry on Windows.
This module 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 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 subkeys to the right and backslash between keys. (Remember that backslashes must be doubled in Erlang strings.) Case is preserved but not significant.
For 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 this module as follows:
Abbreviation 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 can be written as
"\\hklm\\software\\ericsson\\erlang\\5.0"
.
This module uses a current key. It works much like the current directory. From the current key, values can be fetched, subkeys can be listed, and so on.
Under a key, any number of named values can be stored. They have names, types, and data.
win32reg
supports storing of the following types:
REG_DWORD
, which is an integerREG_SZ
, which is a stringREG_BINARY
, which is a binary
Other types can be read, and are 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, for example, %SystemRoot%Windows
. SystemRoot
is
an environment variable, and is to be replaced with its value. Function
expand/1
is provided so that
environment variables surrounded by %
can be expanded to their
values.
For more information on the Windows registry, see consult the Win32 Programmer's Reference.
Types
reg_handle()
As returned by
open/1
.
name() = string() | default
value() = string() | integer() | binary()
Functions
change_key(RegHandle, Key) -> ReturnValue
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
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
RegHandle = reg_handle()
Closes the registry. After that, the
cannot be used.
current_key(RegHandle) -> ReturnValue
RegHandle = reg_handle()
ReturnValue = {ok, string()}
Returns the path to the current key. This is the equivalent of
pwd
.
Notice that the current key is stored in the driver, and can be invalid (for example, if the key has been removed).
delete_key(RegHandle) -> ReturnValue
RegHandle = reg_handle()
ReturnValue = ok | {error, ErrorId :: atom()}
Deletes the current key, if it is valid. Calls the Win32 API
function RegDeleteKey()
. Notice 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
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 default value.
The registry must have been opened in write mode.
expand(String) -> ExpandedString
String = ExpandedString = string()
Expands a string containing environment variables between percent
characters. Anything between two %
is taken for an environment
variable, and is replaced by the value. Two consecutive %
are
replaced by one %
.
A variable name that is not in the environment results in an error.
format_error(ErrorId) -> ErrorString
ErrorId = atom()
ErrorString = string()
Converts a POSIX error code to a string
(by calling erl_posix_msg:message/1
).
open(OpenModeList) -> ReturnValue
OpenModeList = [OpenMode]
OpenMode = read | write
ReturnValue = {ok, RegHandle} | {error, ErrorId :: enotsup}
RegHandle = reg_handle()
Opens the registry for reading or writing. The current key is the
root (HKEY_CLASSES_ROOT
). Flag read
in the mode list
can be omitted.
Use change_key/2
with an absolute path after
open
.
set_value(RegHandle, Name, Value) -> ReturnValue
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 is used. The supported types
are the following:
REG_DWORD
for integersREG_SZ
for stringsREG_BINARY
for binaries
Other types cannot be added or changed.
The registry must have been opened in write mode.
sub_keys(RegHandle) -> ReturnValue
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, as it can be slow.
value(RegHandle, Name) -> ReturnValue
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
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/2
.
Calls the Win32 API function EnumRegValuesEx()
.
See Also
erl_posix_msg
,
The Windows 95 Registry (book from O'Reilly),
Win32 Programmer's Reference (from Microsoft)