Returning to a part of a program

What I would like to accomplish is a program that basically opens three doors, one at a time. Here is the raw program"
os.pullEvent = os.pullEventRaw
local opendoor = "a"
local door2 = "b"
local door3 = "c"
term.clear()
term.setCursorPos(1,1)
write ("Enter Command:")
if input == opendoor then
print "Opening door 1"
-This is where I'm stuck. I would want it to go back to the enter command part of the program after the door opens and keep the local door passcodes so that I can enter another code. Any help would be appreciated, Thank you.

P.S: please try to dumb down your answers, as I am rather new to CC :P/>

This can be achieved using a While loop.
For example:

os.pullEvent = os.pullEventRaw
while true do
local opendoor = "a"
local door2 = "b"
local door3 = "c"
term.clear()
term.setCursorPos(1,1)
write ("Enter Command:")
input = read()
if input == "door 1" then
print("Opening door 1")

  elseif input == "door 2" then
    print("Opening door 2")
    [code]
  elseif input == "door 3" then
    print("Opening door 3")
    [code]
  else
    print("Command not recognised")
  end
end

Once a command has been entered it will respond based on the command then return to the top of the loop when the response (opening a door etc) has been completed.

Try avoiding adding the set strings in the loops, and for the part you got stuck, you can use elseif's for more and more commands

os.pullEvent = os.pullEventRaw
door1Pass = "a"
door2Pass = "b"
door3Pass = "c"

while true do
    term.clear()
    term.setCursorPos(1,1)
    print("Enter Command: ")
    write(" > ")
    input = read()
    if input == door1Pass then
        print("Opening door 1")
        -- Redstone code to open door 1
    elseif input == door2Pass then
        print("Opening door 2")
        -- Redstone code to open door 2
    elseif input == door3Pass then
        print("Opening door 3")
        -- Redstone code to open door 3
    else
        print("Invalid command.")
    end
end

well, I tried the while true do command, but when I enter a, it doesn't show the text "Opening door ". instead, it immediately jumps back to the Enter Command: bit. I would want it to display the Enter Command" bit, but also show the previous text

ah nvm, I figured it out :)/>

Oh woops, just add a sleep(1.5) just before the last end :P/>