Ioan Rogers

Chapter 3. The LCDproc client language

Table of Contents

Opening a session
Command reference
Basic stuff
Screens and widgets
LCDd messages


The LCDproc clients, for example lcdproc, connect over the network to LCDd. In their communication they use a protocol, often refered to as the "widget language". In this chapter the widget language will be discussed.

Opening a session

The essence of talking to LCDd is quite simple. First you will need to connect to the LCDproc port (usually 13666) on the correct IP address (by default localhost). Once you have established the connection you should say "hello", to let LCDd know you are a good guy. It will respond by telling some LCDproc data, like version and screen width and height. Now your session is open and you can start sending 'real' commands.

LCDd can send a number of strings itself. As a response to your commands, it will usually send a "success" string, or a string starting with "huh" in case of any error. See further below for other strings sent by LCDd.

You can test all these commands by opening a TCP/IP connection manually, like with:

 telnet localhost 13666

This way, you can check how the various commands work. It's in this case best to have no other clients. If you do have other clients, you will receive "listen" and "ignore" messages that will disturb your typing.

Command reference

In this section all commands and their parameters are listed, along with the responses you can expect. If you need a space or a special char in a string, you should quote the string with double quotes. If you need to use a double quote, escape it with a backslash. The listing is divided into subsections for

  1. Basic stuff

  2. Screens and widgets

  3. Menu stuff

  4. Miscellaneous

Basic stuff


Opens the session with the LCDd server program. This command is required before other commands can be issued.

The response will be a string in the format:

connect parameter...

The client should read all parameters it needs and store their values. The following parameters are in use:

LCDproc version

Indicates the version number of LCDd.

protocol version

Indicates the widget language version number. This number is only changed when the language of a newer version has become incompatible with the previous version.

wid int

Tells the client the width of the attached display device in characters.

hgt int

Tells the client the height of the attached display device in characters.

cellwid int

How many pixels is a character wide (space between character cells not included)

cellhgt int

How many pixels is a character high (space between character cells not included)


This word is NOT followed by a value ! Hey do we really need this word in the response string ?

client_set -name name

Sets attributes for the current client. The current client is the one from the connection that you send this command on, in other words: yourself.

name is the client's name as visible to a user.

Screens and widgets

screen_add new_screen_id

Adds a screen to be displayed. The screen will be identified by the string new_screen_id, which is used later when manipulating on the screen.

screen_del screen_id

Removes the screen identified by screen_id from the client's screens.

screen_set screen_id attributes...

Sets attributes for the given screen. The following attributes exist:

-name name

Sets the screen's name as visible to a user.

-wid int -hgt int

Sets the size of the screen in characters. If unset, the full display size is assumed.

-priority pri_class

Sets the screen's priority. The following priority classes exist:


The screen will never be visible


The screen is only visible when no normal info screens exists


normal info screen, default priority


an active client


The screen has an important message for the user.


The client is doing interactive input.


a positive integer that maps to priority classes above according to the mapping given in the table below.



1 - 64


65 - 192


193 - ∞


LCDd will only show screens with the highest priority at that moment. So when there are three info screens and one foreground screen, only the foreground screen will be visible. Only background, info and foreground screens will rotate; higher classes do not rotate because their purpose is not suitable for rotation.

-heartbeat { on | off | open }

Changes the heartbeat setting for this screen. If set to open, the default, the client's heartbeat setting will be used.

Changes the screen's backlight setting. If iset to the default value open, the state will be determined by the client's setting. blink is a moderately striking backlight variation, flash is very strinking.

-duration value

A screen will be visible for this amount of time every rotation. The value is in eights of a second.

-timeout value

After the screen has been visible for a total of this amount of time, it will be deleted. The value is in eights of a second. Currently the client will not be informed of the deletion (TODO?).

-cursor { on | off | under | block}

Determines the visibility of a cursor. If on, a cursor will be visible. Depending on your hardware, this will be a hardware or software cursor. The specified cursor shape (block or under) might not be available in which case an other cursor shape will be used instead. Default is off.

-cursor_x int -cursor_y int

Set the cursor's x and y coordinates respectively. If not given, the cursor will be set to the leftmost (-cursor_x) resp. topmost (-cursor_y) position. Coordinates are always 1-based. So the default top-left corner is denoted by (1,1).

widget_add screen_id new_widget_id widgettype [-in frame_id]

Adds a widget to the given screen. The new_widget_id sets the identifier for this widget. The optional -in frame_id places the widget into the given frame. The following widget types exist:


A simple text.


A title bar on top of the screen.


A horizontal bar.


A vertical bar.


A predefined icon. For a list of valid names consult server/widget.c.


A variation of the string type that scrolls the text horizontally or vertically.


A frame with that can contain widgets itself. In fact a frame displays an other screen in it.


A big number. They have a size of 3x4 characters. The special number 10 is a colon, that you can use for a clock. This character is 1x4.

widget_del screen_id widget_id

Deletes the given widget from the screen.

widget_set screen_id widget_id widgettype_specific_parameters

Sets parameters for a widget. Because not all widgets are created equal, the various widget types require different parameters.


x y text

Displays text at position (x,y).



Uses text as the title to display.

hbar , vbar

x y length

Displays a horizontal (hbar) resp. vertical (vbar) starting at position (x,y) that is length pixels wide resp. high.


x y iconname

Displays the icon iconname at position (x,y).


left top right bottom direction speed text

Displays a scroller spanning from position (left,top) to (right,bottom) scrolling text in horizontal (h), vertical (v) or marquee (m) direction at a speed of speed, which is the number of movements per rendering stroke (8 times/second).


left top right bottom width height direction speed

Sets up a frame spanning from (left,top) to (right,bottom) that is width columns wide and height rows high. It scrolls in either horizontal (h) or vertical (v) direction at a speed of speed, which is the number of movements per rendering stroke (8 times/second).


x int

Displays decimal digit int at the horizontal position x, which is a normal character x coordinate on the display. The special value 10 for int displays a colon.

In this section all commands for creation, modification of menus and for interaction with them are described. Although keys may be used for other tasks they are listed here too.

TODO: example for normal (static) menu structure.

Menus may be even be used for wizards (the user is automatically guided through a number of configuration options) by virtue of the options -next and -prev. Here a complete example:

          client_set name Parenttest
          # to be entered on escape from test_menu (but overwritten
          # for test_{checkbox,ring})
          menu_add_item "" ask menu "Leave menus?" -is_hidden true
            menu_add_item "ask" ask_yes action "Yes" -next _quit_
            menu_add_item "ask" ask_no action "No" -next _close_
          menu_add_item "" test menu "Test"
            menu_add_item "test" test_action action "Action"
            menu_add_item "test" test_checkbox checkbox "Checkbox"
            menu_add_item "test" test_ring ring "Ring" -strings "one\ttwo\tthree"
            menu_add_item "test" test_slider slider "Slider" -mintext "" -maxtext "" -value "50"
            menu_add_item "test" test_numeric numeric "Numeric" -value "42"
            menu_add_item "test" test_alpha alpha "Alpha" -value "abc"
            menu_add_item "test" test_ip ip "IP" -v6 false -value ""
            menu_add_item "test" test_menu menu "Menu"
            menu_add_item "test_menu" test_menu_action action "Submenu's action"
          # no successor for menus. Since test_checkbox and test_ring have their
          # own predecessors defined the "ask" rule will not work for them
          menu_set_item "" test -prev "ask"
          menu_set_item "test" test_action -next "test_checkbox"
          menu_set_item "test" test_checkbox -next "test_ring" -prev "test_action"
          menu_set_item "test" test_ring -next "test_slider" -prev "test_checkbox"
          menu_set_item "test" test_slider -next "test_numeric" -prev "test_ring"
          menu_set_item "test" test_numeric -next "test_alpha" -prev "test_slider"
          menu_set_item "test" test_alpha -next "test_ip" -prev "test_numeric"
          menu_set_item "test" test_ip -next "test_menu" -prev "test_alpha"
          menu_set_item "test" test_menu_action -next "_close_"
          menu_set_main ""
client_add_key [ -exclusively | -shared ] key...

Tells the server that the current client wants to make use of the given key(s). If you reserve the key(s) in shared mode, other clients can still reserve these keys too. If you reserve the key(s) in exclusive mode no other client can reserve them again. Key(s) reserved in shared mode will only be returned when a screen of the current client is active. These keys can be used for interaction with a visible screen (default). Key(s) reserved in exclusive mode will be returned regardless of which screen is active. They can be used to trigger a special feature or to make a screen come to foreground. Note that you cannot reserve a key in exclusive mode when an other client has reserved it in shared mode.

client_del_key key...

Ends the reservation of the given key(s).

Adds a new menu item to a menu. The main menu of a client, will be created automatically as soon as the client adds an item. This main menu has an empty id ("") and the name is identical to the name of the client. The options are described under menu_set_item below.


Some menu commands (menu_goto) and options (-prev, -next) assume that menu_ids are unique (at least within a clients menu hierarchy).

menu item types


This item should trigger an action. It consists of simple text.


Consists of a text and a status indicator. The status can be on (Y), off (N) or gray (o).


Consists of a text and a status indicator. The status can be one of the strings specified for the item.


Is visible as a text. When selected, a screen comes up that shows a slider. You can set the slider using the cursor keys. When Enter is pressed, the menu returns.


Allows the user to input an integer value. Is visible as a text. When selected, a screen comes up that shows the current numeric value, that you can edit with the cursor keys and Enter. The number is ended by selecting a 'null' input digit. After that the menu returns.


Is visible as a text. When selected, a screen comes up that shows the current string value, that you can edit with the cursor keys and Enter. The string is ended by selecting a 'null' input character. After that the menu returns.


Allows the user to input an ip number (v4 or v6). When selected, a screen comes up that shows an ip number that can be edited - digit by digit - via left/right (switch digit) and up/down keys (increase/decrease).

This is a submenu. It is visible as a text, with an appended >. When selected, the submenu becomes the active menu.

Removes a menu item item_id from menu menu_id. The menu with the special id "" (i.e. the empty string) is the client's main menu.

Sets parameters for the menu item(s). Each item type knows different parameters.

options for the various menu items

for all item types
-text string

The visible text of the item.

-is_hidden { true | false} (false)

If the item currently should not appear in a menu.

-next successor_id

Sets the menu item to show after hitting the ENTER key when this item is active. This works for all menu item types except menus i.e. also for menu item types without an own screen e.g., checkbox, ring and action.

Special values


Equivalent to -menu_result close: Close the menu.


Equivalent to -menu_result quit: Quit the menu system.


Equivalent to -menu_result none: Keep the item open.

-prev predecessor_id

Sets the menu item to show after hitting the ESCAPE key when this Item is active. This works for all menu item types i.e. also for menu item types without an own screen e.g., checkbox, ring and action.


If you define a predecessor for e.g., a checkbox and its parent menu too, the menu's predecessor is ignored in favor of the checkboxes one.

This option accepts the same special values as the -next option.

-menu_result { none | close | quit} (none)

Sets what to do with the menu when this action is selected: none: the menu stays as it is; close: the menu closes and returns to a higher level; quit: quits the menu completely so you can foreground your app.

-value { off | on | gray }

Set the value of the item.

-allow_gray { false | true} (false)

Sets if a grayed checkbox is allowed.

-value int (0)

Sets the index in the stringlist that is currently selected.

-strings string (empty)

This single string should contain the strings that can be selected. They should be tab-separated (\t).

-value int (0)

Sets its current value.

-mintext string ("") , -maxtext string ("")

The texts at the left and right side of the slider.

-minvalue int (0) , -maxvalue int (100)

The minimum and maximum values of the slider.

-stepsize int (1)

The stepsize of the slider. If you use 0, you can control the movement completely from your client.

-value int (0)

Sets its current value.

-minvalue int (0) , -maxvalue int (100)

The minimum and maximum values that are allowed. If one of them is negative, the user will be able to enter negative numbers too.

TODO: floats!

-value string ("")

Sets its current value.

-password_char string ("")

If used, instead of the typed characters, this character will be visible.

-minlength int (0) , -maxlength int (10)

Sets the minimum and maximum allowed lengths.

-allow_caps { false | true } (true) , -allow_noncaps { false | true } (false) , -allow_numbers { false | true } (false)

(Dis)allow these groups of characters.

-allowed_extra string ("")

The chars in this string are also allowed.

-value string ("")

Set the value of the item, e.g. "" (v4) or ":::ffff:ffff:ffff:ffff:ffff" (v6).

-v6 { false | true } (false)

Changes IP version from default v4.

This is a submenu. It is visible as a text, with an appended '>'. When selected, the submenu becomes the active menu.

-parent parentid

(Re)sets the parent of this menu. Parentid has to be of type menu. This function does not change any menu (neither the old nor the new parent) since this option is normally used with hidden menus. Otherwise use menu_add/del_item. Applying this option is equivalent to second argument of the menu_goto command.

Changes current menu to menu_id. Depending on the configure option --enable-permissive-menu-goto the client may switch to any (if enabled) or his menus only (if not enabled).

The menu item to go to (any menu type e.g. an action or a menu).


Resets the parent of menu_id. This optional parameter can be used to reuse a menu from different places (for wizards etc.). Use it with caution: This may lead to a messy menu structure in particular due to the fact that the menus are not changed !

Sets the entry point into the menu system. Use this to make the server menu invisible. Note that you may only set the menu to your own clients menus unless the configure option --enable-permissive-menu-goto is used. (See menuscreens.c for the menu ids of the server menus.)

The new main menu, restricted to the client's own menus. Special values:

"" (i.e. the empty string)

The client's main menu.


Resets main to the "real" main menu.


Sets the client's backlight state.

output { on | off | int }

Sets the general purpose output on some display modules to this value. Use on to set all outputs to high state, and off to set all to low state. The meaning of the integer value depends on your specific device, usually it is a bit pattern describing the state of each output line.


This command provides information about the driver.


This command does nothing and is always successful. Can be useful to be sent at regular intervals to make sure your connection is still alive.

sleep int

Sleep for the given number of seconds. int must be a positive integer in the range from 1 to 60.


This command is currently ignored on the server side.

LCDd messages

LCDd can send messages back to the client. These messages can be directly related to the last command, or generated for some other reason. Because messages can be generated at any moment, the client should read from the connection at regular intervals. A very simple client could simply ignore all received messages. Not reading the messages will cause trouble !


This is the reponse to a command in case everything went ok.

huh? error_description

This is the response to a command in case something has gone wrong. The description is not meant to be parsed, it's only meant for the programmer of the client. It might be that your command has only been partially executed, for example if you try to reserve 3 keys, and one fails. Your client might need to undo its actions completely.

listen screen_id , ignore screen_id

The screen with the screen_id given is now visible on the display (listen) or it is not visible anymore on the display (ignore).

key key

This message will be sent if there was a keypress that should be delivered to the current client.

The user did something with a client supplied menu. The type of event can be:

select (action)

The item was activated.

update (checkbox, ring, numeric, alpha)

The item was modified by the user, so LCDd sends an updated value.

plus (slider) , minus (slider)

The slider was moved to left (minus) or right (plus), so LCDd sends an updated value.


This item has been entered, which means it is currently active on the screen. The client could now for example update the value of the item. If it is a menu, it may be needed to update the values of the items in it too, because they may be visible too.


This item has been left, so it is currenly not the (main) active item anymore.

Multiple messages may be generated by one action of the user.

8 POD Errors

The following errors were encountered while parsing the POD:

Around line 475:

You forgot a '=back' before '=head2'

Around line 533:

'=item' outside of any '=over'

Around line 592:

You forgot a '=back' before '=head2'

You forgot a '=back' before '=head2'

You forgot a '=back' before '=head2'

Around line 599:

=back without =over

Around line 601:

'=item' outside of any '=over'

Around line 744:

'=item' outside of any '=over'

Around line 825:

You forgot a '=back' before '=head2'

Around line 829:

=back without =over