Script question

Shell Programming and Scripting
1

I know some tricks like this :

echo "                         E"; sleep 0.1; clear;  
echo "                         Er"; sleep 0.1; clear;  
echo "                         Err"; sleep 0.1; clear; 
echo "                         Erro"; sleep 0.1; clear; 
echo "                         Error "; sleep 0.1; clear;
 echo "                         Error P"; sleep 0.1; clear; 
echo "                         Error Pl"; sleep 0.1; clear; 
echo "                         Error Ple"; sleep 0.1; clear; 
echo "                         Error Plea"; sleep 0.1; clear; 
echo "                         Error Pleas"; sleep 0.1; clear; 
echo "                         Error Please "; sleep 0.1; clear; 
echo "                         Error Please T"; sleep 0.1; clear; 
echo "                         Error Please Tr"; sleep 0.1; clear; 
echo "                         Error Please Try "; sleep 0.1; clear;
 echo "                         Error Please Try A"; sleep 0.1; clear; 
echo "                         Error Please Try Ag"; sleep 0.1; clear;
 echo "                         Error Please Try Aga"; sleep 0.1; clear;
 echo "                         Error Please Try Agai"; sleep 0.1; clear
;echo "                         Error Please Try Again"; sleep 0.1; clear;
echo "                         Error Please Try Again."; sleep 0.1; clear; 
echo "                         Error Please Try Again.."; sleep 0.1; clear; 
echo "                         Error Please Try Again..."; sleep 1; clear;

In order to do something a bit more surprising I done this, but I have a big question. Some programs like airodump -ng use to display the characters and change some variables between them and then show them to us without to really change something, I mean to clear the screen or something like that. As you see in the screenshot, airodump-ng changes the number of data and th number of packets and other things and nothing else is moving.I mean neither the screen is cleaned nor there is a command like sleep.How is this possible to be done with the help of a script?

2

You can use escape characters with VT100 emulation -

# Next line: in vi, use control V first to add an escape sequence and
# then control [ for <ESC> (^[=<ESC>)
echo -n "[19;1H $counter"
# DCL: "<ESC>[19;1H" UNIX: "^[[19;1H"
# Moves cursor to line 19 position 1 on screen

#!/bin/csh -f
clear
echo "^[[15;1H Here I am"
sleep 3
echo -n "^[[10;15H Now I am here."
sleep 3
echo -n "^[[20;20H Hey, down here."
sleep 3
echo ""
exit

Note that the ^[ is made in vi editor with Control-V and then Control-[

3

Ansi Escape Sequences