_nya.lua

function keys(t)
  local keylist = {}
  for k in pairs(t) do
    table.insert(keylist, k)
  end
  local i = 0
  return function()
    i = i + 1
    return keylist[i]
  end
end

function addext(exts, mid)
  mid = mid or ''
  return function(cmd)
    if cmd:match('%.') then
      return false
    end

    local variation={}
    local cmdl=cmd:lower()
    for ext, _ in exts do
      variation[ cmdl .. mid .. ext:lower() ] = true
    end

    local path='.;' .. os.getenv('PATH')

    for path1 in path:gmatch('[^;]+') do
      for fname in nyaos.dir(path1) do
        if variation[ fname:lower() ] then
          return fname
        end
      end
    end
  end
end

function nyaos.filter2.ext(cmdline)
  return cmdline:gsub('^%S+',  addext(os.getenv('PATHEXT'):gmatch('[^;]+')))
end

function nyaos.filter.ext(cmdline)
  return cmdline:gsub('^%S+',  addext(keys(nyaos.suffix), '.'))
end

function nyaos.filter.luacode(cmdline)
  return cmdline:gsub('%%(%b())', function(m)
    local status, result = pcall( loadstring('return '..m) )
    if status then
      return result
    end
    print('Ignore invalid Lua expression: '..m)
  end)
end

function nyaos.filter.command(cmdline)
  return cmdline:gsub('$(%b())', function(m)
    return nyaos.eval(m:sub(2,-2))
  end)
end