amartos / luashell

A very simple Lua interpreter + shell in C++

Luashell

A very simple Lua interpreter + shell implementation in C++, as a demo. It currently depends on Lua version 5.4 and GNU’s readline library.

Configuration

The interpreter loads the file located at $LUASHELL_CONFFILE if defined, or $XDG_CONFIG_HOME/luashell/config.lua, if it exists, before execution of any script or the shell’s prompt.

Environment

The interpreter globals are:

name	default value	description	types
CONFFILE	$XDG_CONFIG_HOME/luashell/config.lua	config file path
HISTFILE	$XDG_DATA_HOME/luashell/history	history file path	str, str f()
PROMPT	>>>	prompt string	str, str f()
BANNER		banner string	str, str f()

Definition priorities

Each of these globals are first fetched from the environment, where their name is prefixed with LUASHELL_ (example: LUASHELL_CONFFILE). The default values are used if they are not defined or empty.

The configuration file is loaded after fetching the environment values, thus they can be redefined in it using the name listed in the table above. Note redefinition of globals with an empty types value in the table do not matter at this stage (see the next section).

Finally, they can be redefined in the shell or the script itself, using the names in the table, but the given values won’t persist between sessions.

Globals’ values types

The types column contains a comma-separated list of types that the shell expects to find in the variable. If the type is of the form returnType f(argType, argType, ...), the value may be a Lua function of the described prototype (the name f does not matter).

If no types are defined, the variable expects a string and its redefinition is only considered if it is done in the environment. The value is still accessible and modifiable from the shell/script/config file, but this won’t affect the interpreter at all.

For a list of available types (applicable to returnType and argType), see the types used by Lua. Their name may be shortened in the table, for example str for string. The following types are additional to this list:

type	Lua type	description
int	number	a number that will be truncated

luashell's Issues

Signals are not handled

The shell should handle signals sent through keyboard, at least:

• SIGINT (ctrl-c)
  • do not interrupt the shell itself
  • interrupt running commands
• SIGSTOP (ctrl-z)
• SIGCONT (jobs control)

SIGSEGV error when a global holds a non-returning function

If a predefined global expects (among other types) a function returning a value, and that function does not return any value, the shell crashes with a SIGSEGV signal.

Implement more unit tests

• Globals
  • definition from environment
  • definition from script
  • definition from shell
  • no definition
  • wrong definition
• Interactive mode
  • Lua interpreter launched
  • Lua errors handling (proper error messages printing?)
  • Signals handling (see #1)
• Interpreter mode
  • Identification of shebangs (see #5)
  • Proper script execution
  • No printing of globals (PROMPT, BANNER, ...)
  • Printing of all CONFFILE loading result
  • No signal handling in interpreter mode (see #1)

Add github actions to the repo

Actions for:

• unit testing
• coverage
• compilation && deployment

No checking of scripts shebangs before execution

add an option to execute simple commands (equivalent to bash's -c)