Turtle Construction

h = fs.open("text","r")

local args = {...}

local myChar = args[1]
local height = 0
local ascending = true

--reset slot selection to 1
turtle.select(1)

--checks to see if it has 2 or more blocks. if it only has one, it will back away from construction until it has been refilled
function checkInventory()
    --checks the current slot
    local amount = turtle.getItemCount()
    if amount>=2 then
        return
    end

    if (turtle.getSelectedSlot()==16) or (turtle.getItemCount(turtle.getSelectedSlot()+1)==0) then
        turtle.back()
        turtle.select(1)
        --once it backs up, it sleeps five seconds at a time and then rechecks if it has been filled
        while turtle.getItemCount()<=1 do
            sleep(5)
        end
        --tries to move forward again
        while (turtle.detect() == true) do
            sleep(1)
        end
        turtle.forward()
        --ready to continue
        return
    end

    if (amount==0) then
        turtle.select(turtle.getSelectedSlot()+1)
    end
end

--tries to move up. if it fails, it waits 5 seconds then tries again.
function up()
    while (turtle.up()==false) do
        sleep(5)
    end
    height = height + 1
end

--tries to move down. if it fails, it waits 5 seconds then tries again.
function down()
    if height==0 then
        return
    end
    while (turtle.down()==false) do
        sleep(5)
    end
    height = height-1
end

--performs the turn at the top/bottom of a column
function turn()
    turtle.turnRight()
    while (turtle.forward() == false) do
        sleep(5)
    end
    turtle.turnLeft()
    down()
end


checkInventory()
line = h.readLine()

while ((line ~= "") and (line ~= nil)) do
    for i=1,string.len(line) do
        checkInventory()
        if (not turtle.detect()) and (string.sub(line,i,i) == myChar) then
            turtle.place()
        end
        --move then check to see if it has enough resources to continue
        if (ascending==true) then
            up()
        else
            down()
        end
    end

    --the column is complete, so we perform a turn
    turn()
    line = h.readLine()
    ascending = not ascending
end

turtle.back()
turtle.back()