Shell Programming and Scripting

As you might have seen from the previous answers (which are all, more or less, glorious hacks) what you want is impossible directly. The reason is that the terminal a typical UNIX session uses is linebased: you enter a command, which prints one or more lines, then you enter the next command.

A UNIX terminal is in principle like an endless roll of paper with a typing device to print on it, like a classic typewriter. In fact the typical "tty"s - "teletypes" - commonly in use when UNIX was created were exactly this: typewriters connected to a computer via a serial line. Modernization put layer on layer of virtualization and abstraction onto this but the basic principle remained.

It is possible to get a little more than that, but that depends on the terminal you use: enter

Code:

# echo $TERM

and you probably get an output like "xterm", "dtterm", "kterm", or similar. These (rather modern, compared to when the terminal system of UNIX was designed) terminals can do more fancy things like reposition the cursor (search for the terms "termcap" and "terminfo" to get more information about how that works), print in various colours and more.

The way they do that is quite unwieldy, though (see the previous posts). This is why this part (the ugly part of the coding) is put away into libraries which can nicely be used from the commandline: the most common library and a de-facto standard in itself is "curses", which i suggest you try to install and use.

If you are interested in using a grahical (instead of text-oriented) tool you could also give "Tcl" with the "Tk" extension a try. "Tcl/Tk" (usually pronounced "tickle-teekay") is a very common and widely used tool for developing GUI-oriented programs. As a scripting language it is relatively easy to learn (about as complicated as shell programming).

I hope this helps.

bakunin

Again a bit of a kludge but as I use tput it should work for other terminal types (eg wyse), the escape sequences hard-coded in previous solutions are specific to VT* compatible terminals.

Note it also works for 2 digit and longer numbers.

The first line ensures the prompt isn't on the bottom line by printing a blank line and then going up.

Code:

printf "\n"; tput cuu 1
printf "Enter the two digits of your sum: "
tput sc
read NUM1
tput rc
read -p "$NUM1 + " NUM2
echo "$NUM1 + $NUM2 = $((NUM1 + NUM2))"

edit: use read -d" " NUM1 to use space instead of CR between 1st and 2nd number