nicembedded / lua-shell

A (prototype) shell attempting to harness the power of Lua for day-to-day command line usage.

lua-shell

lua-shell (working title) is an attempt at harnessing the power of Lua for use as a Unix shell. Thus, the goals of the project are:

• To provide an intuitive interface to external programs, including system utilities such as ls and sudo as well as other CLI tools, in a consistent manner.
• To provide facilities for creating command pipelines in order to take advantage of the Unix philosophy of combining small, specialized programs to complete a complex task.
• To provide an improved REPL, compared to the default one of Lua's interactive interpreter.

The project is still very much a work in progress and is not suitable for practical usage.

Examples

Demo

The following example script demonstrates a couple of the features -- external commands, integration with Lua functionality, subshells, command substitution and stdout redirection -- provided by lua-shell:

function get_ls_args()
	return "-l", "~/projects/lua-shell/"
end

function formatter(prefix) print(prefix .. io.read("*a")) end

ls(get_ls_args())                     -- retrieve file list
  .grep "READ"                        -- filter to find line including 'READ'
  .grep "-oP" "[^ ]+$"                -- filename only
  .sub(formatter) "File found: "      -- add label with our formatter function as a subshell
  .out "/tmp/luashelltest"()          -- redirect to /tmp/luashelltest

myVar = cs(cat "/tmp/luashelltest")   -- command substitution to put contents of file into variable

echo(myVar)()                         -- echo variable with external program

This is the equivalent code in the traditional shell scripting syntax:

function get_ls_args
{
	echo "-l ~/projects/lua-shell"
}

function formatter { echo "$1"$(cat); }

ls $(get_ls_args) |
  grep "READ" |
  grep -oP "[^ ]+$" |
  formatter "File found: " >
  /tmp/luashelltest

myVar=$(cat /tmp/luashelltest)

echo $myVar

rc file

Upon starting the shell, the file ~/.lushrc is automatically executed. This file can be used to set up aliases, settings the prompt and doing other initialization work, just like .bashrc and equivalents. Here is an example .lushrc file:

-- Include luaposix modules and set some global variables.
posix = require("posix")
posix_uts = require("posix.sys.utsname")
utsname = posix_uts.uname()
HOST=utsname.nodename
HOME=os.getenv("HOME")
USER=posix.getlogin()


-- Set up aliases.
ls=ls "--color=always"

-- Set up a table 'git' with a metatable to
-- let us run commands like 'git.status' instead of 'git "status"'.
local _git = git
git = {}
setmetatable(git,
{
	__index = function(t, func) return _git(func) end
})

-- Utility function to reload this file.
function rrc()
	dofile(HOME .. "/.lushrc")
	print("RC file reloaded.")
end

-- Make the prompt path a little prettier by substituting
-- the home part of the path with '~'.
function make_pretty_path()
	return posix.getcwd():gsub(HOME, "~")
end

-- Extract the currently checked out branch of the Git repository we're in.
-- stderr is simply redirected to stdout so that, in case we're not in a Git repository,
-- the error message is just piped to grep but won't match.
function get_git_branch()
	branch = cs(err(git.branch) . grep "-oP" "\\* .+$" . grep "-oP" "[^* ]+")
	if branch == "" then
		return ""
	else
		return string.format(" [%s]", branch)
	end
end

-- Actually set the prompt. This function gets called each time the prompt is printed.
-- Escape sequences are ANSI colours.
function settings.prompt()
	return string.format("\x01\x1b[32;1m\x02[%s@%s:%s]%s [%s]\n\x01\x1b[31;1m\x02$ \x01\x1b[0m\x02",
			USER, HOST, make_pretty_path(), get_git_branch(), os.date("%H:%M:%S"))
end

License

See LICENSE.md.