I'm using chez-scheme and I can't find a way to clear the screen completely. (If someone knows a better way than printing I'd be interested in that too but it's not my question here)
From what I can find clearing the screen by ^L (control-L) or giving the clear command (in bash at least) is equivalent to outputting ASCII character 12: Form feed.
However, printing this does nothing. If I use (display (integer->char 12)) it just prints a newline. Another way to encode this character is \f (analogous to \n for newline), but in Python print("\f") as well as in Scheme (display "\f") is just a newline.
Is my understanding of the meaning of ASCII 12 just wrong, or are implementations lacking?
Is there any way to clear the screen that should work across languages, analogous to \n for a newline?
If you want to clear the screen, the "ANSI" sequence in a printf
\033[2J
clears the entire screen, e.g.,
printf '\033[2J'
The command-line clear program uses this, along with moving the cursor to the "home" position, again an "ANSI" sequence:
\033[H
The program gets the information from the terminal database. For example, for TERM=vt100, it might see this (using \E as \033):
clear=\E[H\E[J$<50>
(the $<50> indicates padding needed for real VT100s). You might notice that the 2 is absent from this string. That is because the cursor is first moved to the home (upper left) position, and the 2 (entire screen) is not necessary. Eliminating that from the string made VT100s a little faster.
On the other hand, if you just want to reset the terminal, you can use the VT100-style RIS:
\033c
but that has side-effects, besides not being in ECMA-48. These bug reports were for side-effects of \033c:
Further reading:
CSI Ps J Erase in Display (ED).
Ps = 0 -> Erase Below (default).
Ps = 1 -> Erase Above.
Ps = 2 -> Erase All.
Ps = 3 -> Erase Saved Lines (xterm).