Lua/Lua syntax

Camera scripting using LUA

Some new CHDK builds includes LUA as additional scripting language, this page is intended to give a overview of the syntax of LUA usage in CHDK scripts.

This is work in process...

LUA Syntax short manual

• Lua is a case-sensitive language
• Lua is dynamically typed, variables in LUA do not have types, there are no type definitions for variables in LUA.

Keywords:

and		break		do		else		elseif		end		false		for
function	if		in		local		nil		not		or		repeat
return		then		true		until		while

Special CHDK keywords:

click		press		release		shoot		sleep		require

Variables:

• Lower latin letter from a to z
• Upper latin letter from A to Z
• 32 bit signed integer
• Variables have to start with a character or an underscore

Strings

• Strings are bordered by quotation marks " " (only single lines) or square brackets [[ ]] .
• Strings can be concatenated by two dots ..

Tables

• ToDo

Libraries

Libraries are standard LUA scripts placed either in CHDK\SCRIPTS or CHDK\LUALIB, called within a script with

require "libname"

where libname is the filename of the library file without '.lua' suffix.

This means one can create a library of functions and recycle this lib in scripts with a call to require "libname".

Library files were first searched from CHDK/SCRIPTS, and then if not found, from CHDK/LUALIB; if a file with the required name is available in both folders, the one from the first folder (CHDK\SCRIPTS) is used.

Comments:

Comments starts with a double hyphen -- anywhere outside a string.

If the text immediately after -- is not an opening square bracket [ , the comment is a short comment, which runs until the end of the line. Otherwise, it is a long comment, which runs until the corresponding closing square bracket ] . Long comments are frequently used to disable code temporarily.

Sample:

print("Hello CHDK !") -- this is a line with a comment at the end

The script header:

The header of a LUA script is the same as on a uBASIC script, packed into a long comment - the script parser interpretes this the same way in LUA as in uBASIC.

A Sample LUA header:

--[[
rem 20080815 test script by xxx
@title test script
@param a Duration (min)/-1 disable
@default a -1
@param b Duration (sec)/n of seqs
@default b 5
@param h Endless?
@default h 0
--]]

Script Commands

All uBASIC script commands are also available in LUA, almost with the same syntax.

See the Scripting Tutorial for a more complete explanation and for the usage of all commands.

If an execution/parse error occurs a message with a short explanation and the line number is shown in the mini console.