win32reg
win32reg provides access to the registry on Windows
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.
Functions
change_key(RegHandle, Key) -> ReturnValue
RegHandle = term()
Key = string()
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 = term()
Key = string()
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)-> ReturnValue
RegHandle = term()
Closes the registry. After that, the RegHandle
cannot
be used.
current_key(RegHandle) -> ReturnValue
RegHandle = term()
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
RegHandle = term()
ReturnValue = ok | {error, ErrorId}
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
RegHandle = term()
ReturnValue = ok | {error, ErrorId}
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
String = 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
ErrorId = atom()
ErrorString = string()
Convert an POSIX errorcode to a string (by calling erl_posix_msg:message
).
open(OpenModeList)-> ReturnValue
OpenModeList = [OpenMode]
OpenMode = read | write
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
Name = string() | default
Value = string() | integer() | binary()
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
ReturnValue = {ok, SubKeys} | {error, ErrorId}
SubKeys = [SubKey]
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
Name = string() | default
ReturnValue = {ok, Value}
Value = string() | integer() | binary()
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
ReturnValue = {ok, ValuePairs} | {ok, ErrorId}
ValuePairs = [ValuePair]
ValuePair = {Name, Value}
Name = string | default
Value = string() | integer() | binary()
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)