Simple Menu

local tab = {
    "Hi",
    "Goodbye",
    "Hello",
    "Exit",
    'last',
}
local sX, sY = term.getSize()

local function getLongest( _table )
    local longest = 0
    for index, text in pairs( _table ) do
        longest = #text > longest and #text or longest
    end
    return longest + 1
end

local function menu( _table, startX, startY )
    local function printMenu( _table, long, sel, yPos )
        --for index, text in pairs( _table ) do
        --  term.setCursorPos( startX, startY + index - 1 )
        --  write( ( index == sel and '[ ' or '  ' ) .. text .. string.rep(' ', long - #text) .. ( index == sel and ']' or ' ' ) )
        --end
        for i = 1, sY do
            if _table[i + yPos - 1] then
                local tmp = _table[i + yPos - 1]
                term.setCursorPos( startX, startY + i - 1 )
                write( ( i + yPos - 1 == sel and '[ ' or '  ' ) .. tmp .. string.rep(' ', long - #tmp) .. ( i + yPos - 1 == sel and ']' or ' ' ) )
            else break end
        end
    end

    local longest = getLongest( _table )
    local sel = 1
    local yPos = 1

    while true do
        printMenu( _table, longest, sel, yPos )
        local e, key = os.pullEvent()
        if e == "key" or e == "mouse_scroll" then
            if key == keys.up or key == -1 then
                -- up
                if yPos > 1 then
                    yPos = yPos - 1
                end
                if sel > 1 then
                    sel = sel - 1
                end
            elseif key == keys.down or key == 1 then
                -- down
                if sel < #_table then
                    sel = sel + 1
                end
                if yPos < #_table - 18 and sel >= 20 then
                    yPos = yPos + 1
                end
            elseif key == keys.enter then
                return _table[sel], sel
            end
        end
    end
end

term.clear()

while true do
    local sOption, sNumb = menu( tab, (sX-getLongest(tab))/2, 1 )

    term.clear() term.setCursorPos( 1, 1 )

    if sOption == "Hi" then
        print( "Hello there! :D" )
    elseif sOption  == "Goodbye" then
        print( "Why are you going? :(" )
    elseif sOption == "Hello" then
        print( "Oh hello again :>" )
    elseif sOption == "Exit" then
        print( "Cheers :<" )
        break
    end
    sleep(2)
    term.clear() term.setCursorPos( 1, 1 )
end