Using Lua Command Line Client (CLI)

November 07, 2024

Lua is an amazing, performant, and very lightweight scripting language, and why not to use these advantages for daily automation jobs? Lua package shipped with interpreter and can be very easily used from the command line.

Installation of Lua CLI is very straightforward; for Linux, you might have root privileges or use the sudo command:

Ubuntu or Debian-based GNU Linux

apt install lua

Fedora or RPM-based GNU Linux

dnf install lua

Arch GNU Linux

pacman -S lua

Mac OS with brew

brew install lua

Microsoft Windows Lua binaries can be found on SourceForge.

After installing or compiling Lua from source code, lua (for Microsoft Windows, lua.exe or similar) is available on the system.

Tip

Be sure that lua is located in the PATH environment variable. File can start with a line and execute it on any Unix-like platform.

#!/usr/bin/env lua

Lua skips the first line of a file if it starts with #.

lua
Lua 5.4.7  Copyright (C) 1994-2024 Lua.org, PUC-Rio
>

Output of the lua command, it runs the interpreter in interactive mode default. Symbol > means: waiting for the input. Here Lua language commands can be entered like:

> 1 + 23
24
> "hello" .. " " .. "world"
hello world
>

To quit interactive mode, press on the keyboard Ctrl+D.

Every line is interpreted as single chunk, so this means every statement has its own scope.

Consider:

lua
> local x = 10
> local y = 32
> x + y
stdin:1: attempt to perform arithmetic on a nil value (global 'x')
stack traceback:
        stdin:1: in main chunk
        [C]: in ?

To enter multiline code, use the do-end statement:

lua
> do    
>> local x = 10
>> local y = 32
>> print(x + y)
>> end
42
>

Notice the symbol >> means continue the statement. Other ways to enter multi-statement command in single line use ; (semicolon) as statements separator.

If this is still not clear, read the post about chunks.

lua 
> local x = 10; local y = 32 print(x + y);
42
>

Options aka flags¶

lua command has some options to run with; to see help, enter into terminal lua --help:

lua --help
lua: unrecognized option '--help'
usage: lua [options] [script [args]]
Available options are:
  -e stat   execute string 'stat'
  -i        enter interactive mode after executing 'script'
  -l mod    require library 'mod' into global 'mod'
  -l g=mod  require library 'mod' into global 'g'
  -v        show version information
  -E        ignore environment variables
  -W        turn warnings on
  --        stop handling options
  -         stop handling options and execute stdin

-e: execute statement;

lua -e 'print(400 + 10 * 4)'
440
>

-i: interactive mode will be active after execution of script.lua, and you can continue entering commands.

lua -i tt.lua 
Lua 5.4.7  Copyright (C) 1994-2024 Lua.org, PUC-Rio
>

-l mod extra 3rd party any home-made module mod can be included in the script.

Lua 5.4.7  Copyright (C) 1994-2024 Lua.org, PUC-Rio
> print(socket)
table: 0x1a50350
>

-l g=mod same as above, but mod will be stored in the variable g, (This form was introduced in release 5.4.4):

lua -i -l soc=socket 
Lua 5.4.7  Copyright (C) 1994-2024 Lua.org, PUC-Rio
> print(soc)
table: 0x11524c0
>

-v prints the version of Lua and exits the program;

lua -v
Lua 5.4.7  Copyright (C) 1994-2024 Lua.org, PUC-Rio

-E ignore environment variables; This flag is a bit confusing. This means that you can still read environment variables with function os.getenv('USER'), but variables such as LUA_PATH and LUA_CPATH are ignored.

Example:

lua -E -l socket
lua: module 'socket' not found:
        no field package.preload['socket']
        no file '/usr/local/share/lua/5.4/socket.lua'
        no file '/usr/local/share/lua/5.4/socket/init.lua'
        no file '/usr/local/lib/lua/5.4/socket.lua'
        no file '/usr/local/lib/lua/5.4/socket/init.lua'
        no file './socket.lua'
        no file './socket/init.lua'
        no file '/usr/local/lib/lua/5.4/socket.so'
        no file '/usr/local/lib/lua/5.4/loadall.so'
        no file './socket.so'
stack traceback:
        [C]: in function 'require'
        [C]: in ?

It cannot find the socket module because LUA_PATH is ignored. This cause the error.

-W turn warnings on; the built-in function warn will start to output messages. I have a post about warnings.
-, – both work the same as in the bash command line. Check the GNU bash manual for more details.

References¶

Feedback

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