换页不清除屏幕

Question

I've discovered the Ada programming language recently, but the problem exists in the C programming language as well. The form feed does not work as expected.

Ada Example:

with Ada.Text_IO; use Ada.Text_IO;

procedure Main is
begin
  New_Page;
end Main;

Same in C:

#include <stdio.h>

int main (void) {
  printf ("\f");
  return 0;
}

Both result only in a new line on XTerm as well as Linux console (both with zsh). They should clear instead the screen as an Ctrl-L does.

When called with

# ./main | cat -A

I get a

^L

But if I type a

# cat -A

and type a

Ctrl-L

I get a

^L

too.

Does anyone know how to make the form feed work as a Ctrl-L?

Thanks for your help!

Answer 1

According to this article the proper way to clear the screen is printf("\\033[2J"); (provided your terminal supports ANSI escape sequences and is VT100 -compatible). I can confirm that this works on Linux Mint using GNOME Terminal, and on Windows using xterm and PuTTY.

^L clearing the screen doesn't look like a portable convention. For example on HP-UX with the POSIX shell, passing ^L to the shell doesn't do anything. This seems more like a bash occurrence.

Printing \\f will clear the screen with some terminals but not others. For example logging to a Red Hat host from Windows, I can clear the screen with printf("\\f"); in PuTTY but not in xterm (I get a blank line in the latter case).

Answer 2

I tried to edit @Nobilis' answer to add an Ada version, but I think my edit got lost when the screen was cleared, so here's another try:

with Ada.Text_IO; use Ada.Text_IO;

procedure Main is
begin
  Put (ASCII.ESC & "[2J");
end Main;

In a larger program, you might need to follow it with a "Flush;" call since the above could get buffered by the I/O packages, which probably won't realize this is a special terminal command. (Same in C, I think: fflush(stdout); .)