term: ESC[2J, so clear(1) can actually clear

The terminal understood SGR and nothing else, so there was no way to erase the
screen - printing 18 newlines only scrolls the history up out of sight.
term_erase_all blanks the buffer, resets the colours, homes the cursor and
repaints; the CSI parser routes 'J' to it, and clear(1) is four putc calls.

1 files changed, 10 insertions, 0 deletions

diff --git a/usr/clear.c b/usr/clear.c
new file mode 100644
index 0000000..76ee4dc
--- /dev/null
+++ b/usr/clear.c
@@ -0,0 +1,10 @@
+#include "gbos.h"
+/* clear: erase the screen and home the cursor.
+ * Emits ESC[2J, which the terminal understands (see term.asm term_erase_all) -
+ * printing 18 newlines would only scroll the history up, not clear it. */
+void main(void) {
+    putc(27);
+    putc('[');
+    putc('2');
+    putc('J');
+}