receive.lua

local modem = peripheral.find("modem")
rednet.open(peripheral.getName(modem))

local function WriteFile(message)
    print("Writing received file...")
    local programName = message:match("%S+")
    local actualMsg = message:sub(#programName+2)

    if fs.exists(programName) then print("File already exists. Overwriting...") end
    local file = fs.open(programName, "w")
    file.write(actualMsg)
    file.close()
    print("Wrote file " .. programName .. ".")
end

local function Execute(message)
    local path = message:match("%S+")
    local args = message:sub(#path+2)
    os.run({}, path, args)
end

local function ProcessMessage(message)
    local cmd = message:match("%S+")
    local cmdLower = cmd:lower()
    local justMessage = message:sub(#cmd+2)
    if cmdLower == "file" then
        WriteFile(justMessage)
    end
    if cmdLower == "exec" then
        Execute(justMessage)
    end
end

local function AwaitMessage()
    print("\nAwaiting Message...")
    local computerId, msg, protocol = rednet.receive()
    print("Received Message..")
    ProcessMessage(msg)
end

while true do
    AwaitMessage()
end