Lua for Programmers Part 4: Tips and Tricks
Posted on September 09, 2012 in Tutorials
- Part 1: Language Essentials, covers fundamental syntax and concepts such as operators, loops, and functions.
- Part 2: Data and Standard Libraries, covers Lua's built-in data types and some of the standard libraries.
- Part 3: More Advanced Concepts, deals with things like variable scope, advanced functions, and file loading.
- Part 4: Tips and Tricks, the current part; a collection of small things that you may find useful.
Command Line Arguments
Command line arguments are stored in the
arg table. For example, if we had the script
print(arg[-1], arg) for i, v in ipairs(arg) do print(v) end
And we ran it via
lua foo.lua arg1 arg2 arg3, the output would be:
lua foo.lua arg1 arg2 arg3
arg[-1] is the name of the interpreter/program, generally
arg is the name of the file run. All entries after this are the command line arguments; this allows you to iterate over them as shown in the example.
... in Files
Since files are loaded as functions, it makes sense that you can use
... inside of them. If we have a file called
print(...) -- prints all arguments given to this file's function
And then we load it like this:
loadfile("bar.lua")(1, 2, 3, 4)
The output will be
1 2 3 4.
As for the other functions,
dofile sends no arguments, and
require sends a single argument with the path it was given:
require("bar") -- "bar" is the output require("folder.subfolder.bar") -- "folder.subfolder.bar" is the output
If you use
... in the entry-point file (this would be
foo.lua if you executed
lua foo.lua, for example) you'll get a list of command line arguments. So if we were to run
lua bar.lua arg1 arg2 arg3, the output would be
arg1 arg2 arg3.
_G is a global table which holds all global variables. Here's an example:
a = 3 print(_G.a) -- 3 _G.b = 4 print(b) -- 4 print(_G._G == _G) -- true
Well, that's it for now. If you've got any suggestions for things that could be added, I'd love hear them.
Thanks for reading the series, I hope it's been of use to you.
Tagged in Lua, programming
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