How do command line tools change their output after outputting it?

Question

I\'ve noticed that a lot of command line tools, wget for example, will show progress as a number or progress bar that advances as a process is completed. While the question isn\

Answer 1

Just print a CR (without a newline) to overwrite a line. Here is an example program in perl:

#!/usr/bin/env perl

$| = 1;

for (1..10) {
  print "the count is: $_\r";
  sleep(1)
}

I've also disabled output buffering ($| = 1) so that the print command sends its output to the console immediately instead of buffering it.

Haskell example:

import System.IO
import Control.Monad
import Control.Concurrent

main = do
  hSetBuffering stdout NoBuffering
  forM_ [1..10] $ \i -> do
    putStr $ "the count is: " ++ show i ++ "\r"
    threadDelay 1000000