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Clearing Parts of the Screen
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There are several terminal capabilities for clearing parts of the
screen to blank. All display terminals support the `cl' string, and
most display terminals support all of these capabilities.
`cl'
String of commands to clear the entire screen and position the
cursor at the upper left corner.
`cd'
String of commands to clear the line the cursor is on, and all the
lines below it, down to the bottom of the screen. This command
string should be used only with the cursor in column zero; their
effect is undefined if the cursor is elsewhere.
`ce'
String of commands to clear from the cursor to the end of the
current line.
`ec'
String of commands to clear N characters, starting with the
character that the cursor is on. This command string is expected
to leave the cursor position unchanged. The parameter N should
never be large enough to reach past the right margin; the effect
of such a large parameter would be undefined.
Clear to end of line (`ce') is extremely important in programs that
maintain an updating display. Nearly all display terminals support this
operation, so it is acceptable for a an application program to refuse to
work if `ce' is not present. However, if you do not want this
limitation, you can accomplish clearing to end of line by outputting
spaces until you reach the right margin. In order to do this, you must
know the current horizontal position. Also, this technique assumes
that writing a space will erase. But this happens to be true on all
the display terminals that fail to support `ce'.