cls - clear the screen
Cls clears the screen of the userís terminal. The optional argument
NumExpr is unused but may appear for the sake of compatibility. It determines
the proper way of clearing the screen by examining the environment variable TERM
and looking up the terminal in the systemís terminal capability database, either
/etc/termcap or /usr/lib/terminfo.
is unable to determine the terminal type or is unable to access
the terminal capability database, it does nothing.
If the environment variable BASECHO is set to a non-null value
when a Basmark QuickBASIC program begins executing,
the BASIC input/output facility operates differently in order
to support half-duplex terminals such as the IBM 3278.
In this modified behavior of the input/output facility, the terminal
modes are not altered.
may fail to work properly under some circumstances because of
post-processing by the terminal driver.
The Basmark QuickBASIC Programmerís Manual