lua is the stand-alone Lua interpreter.
It loads and executes Lua programs,
either in textual source form or
in precompiled binary form.
(Precompiled binaries are output by
luac, the Lua compiler.)
lua can be used as a batch interpreter and also interactively.
options (see below)
are executed and then
the Lua program in file
script is loaded and executed.
args are available to
script as strings in a global table named
arg. If these arguments contain spaces or other characters special to the shell,
then they should be quoted
(but note that the quotes will be removed by the shell).
The arguments in
arg start at 0,
which contains the string
script. The index of the last argument is stored in
arg.n. The arguments given in the command line before
script, including the name of the interpreter,
are available in negative indices in
At the very start,
before even handling the command line,
lua executes the contents of the environment variable
LUA_INIT, if it is defined.
If the value of
LUA_INIT is of the form
filename is executed.
Otherwise, the string is assumed to be a Lua statement and is executed.
Options start with
- and are described below.
You can use
-- to signal the end of options.
If no arguments are given,
-v -i is assumed when the standard input is a terminal;
- is assumed.
In interactive mode,
lua prompts the user,
reads lines from the standard input,
and executes them as they are read.
If a line does not contain a complete statement,
then a secondary prompt is displayed and
lines are read until a complete statement is formed or
a syntax error is found.
So, one way to interrupt the reading of an incomplete statement is
to force a syntax error:
; in the middle of a statement is a sure way of forcing a syntax error
(except inside multiline strings and comments; these must be closed explicitly).
If a line starts with
lua displays the values of all the expressions in the remainder of the
line. The expressions must be separated by commas.
The primary prompt is the value of the global variable
_PROMPT, if this value is a string;
otherwise, the default prompt is used.
Similarly, the secondary prompt is the value of the global variable
to change the prompts,
set the corresponding variable to a string of your choice.
You can do that after calling the interpreter
or on the command line
(but in this case you have to be careful with quotes
if the prompt string contains a space; otherwise you may confuse the shell.)
The default prompts are "> " and ">> ".