playerswhohaveenteredmybasedetectioninator

Sensor = peripheral.wrap("top")
PlayerNamesTable = {}

function TableContains(table, item)
    for key, value in pairs(table) do
        if (value == item) then
            return true
        end
    end

    return false
end

function CheckPlayerNotAddedAndThenAdd(playerName)
    if (TableContains(PlayerNamesTable, playerName) == false) then
        table.insert(table, playerName)
    end
end

function IsEmpty(str)
    return str == nil or str == ''
end

function Main()
    while true do
        local playerNames = Sensor.getPlayerNames()

        for key, name in pairs(playerNames) do
            CheckPlayerNotAddedAndThenAdd(name)
        end

        term.clear()

        for key, playerName in pairs(PlayerNamesTable) do
            print(playerName)
        end

        os.sleep(2)
    end
end

Main()