feat: add builtins clear, exec and cat (#208)

* feat: add clear and exec command

* docs: add builtins to changelog

* feat: add cat command

CHANGELOG.md

@@ -75,6 +75,7 @@ disables commands being added to history.
 - A new and "safer" event emitter has been added. This causes a performance deficit, but avoids a lot of
 random errors introduced with the new Lua runtime (see [#197])
 - `bait.release(name, catcher)` removes `handler` for the named `event`
+- `exec`, `clear` and `cat` builtin commands
 
 [#197]: https://github.com/Rosettea/Hilbish/issues/197
 

nature/commands/cat.lua

@@ -0,0 +1,25 @@
+local commander = require 'commander'
+local fs = require 'fs'
+
+commander.register('cat', function(args)
+	local exit = 0
+
+	if #args == 0 then
+		print [[
+usage: cat [file]...]]
+	end
+
+	for _, fName in ipairs(args) do
+		local f = io.open(fName)
+		if f == nil then
+			exit = 1
+			print(string.format('cat: %s: no such file or directory', fName))
+			goto continue
+		end
+
+		io.write(f:read '*a')
+		::continue::
+	end
+	io.flush()
+	return exit
+end)

nature/commands/clear.lua

@@ -0,0 +1,7 @@
+local ansikit = require 'ansikit'
+local commander = require 'commander'
+
+commander.register('clear', function()
+	ansikit.clear(true)
+	ansikit.cursorTo(0, 0)
+end)

nature/commands/exec.lua

@@ -0,0 +1,5 @@
+local commander = require 'commander'
+
+commander.register('exec', function(args)
+	hilbish.exec(args[1])
+end)