read function has second argument.

http://www.computercraft.info/wiki/Read
The read function in the wiki doesn't specify the second argument you can input to it. This argument is a table that contains strings theses strings will are then used with the up / down keys in the shell for example to select a input that was made previously.

local tLast = {}
while true do
    local input = read(nil,tLast)
    tLast[#tLast + 1] = input
end