This system variable determines the line spacing for output generated with ? and ??.
_PSPACING = nLineSpacing
You can set _PSpacing to anything you want, as long as it's between 1 and 3. Only the integer part of the value is significant—no line-and-a-half spacing allowed.
SET PRINT TO test.txt
SET PRINT ON
_PSPACING = 2
FOR ncnt = 1 TO 20
_PCOLNO = 2*ncnt
?? "Line "+PADL(ncnt,2)
?
ENDFOR
SET PRINT OFF
SET PRINT TO
* Note that the line spacing is doubled