You have to write to new file and than delete old one and rename new one, if necessary. Her's a pseudo code

lhErrorLog = FOPEN(<Existing Log file>)
lhNewErrorLog = FCREATE(<New log File>,12)
lnCounter = 0
DO WHILE NOT FEOF()
  lcBuffer = FRGET(lhErrorLog, 256)
  lnCounter = lnCounter + 1 
  IF lnCounter > 1000
    FFPUT(lhNewErrorLog, lcBuffer)
  ENDIF
ENDDO
...

>I create logfile entrys with a routine like this

>	lsErrorLog = "c:\mylog.Log"
>	lhErrorLog = FOPEN(lsErrorLog, 12)
>
>	* create if not there
>	IF lhErrorLog < 0
>	  lhErrorLog = FCREATE(lsErrorLog)
>	ENDIF
>
>	
>	  = FSEEK(lhErrorLog, 0, 2)
>	  = FPUTS(lhErrorLog, "Datum   : " + DTOC(DATE())    + " " + TIME())
>	  = FPUTS(lhErrorLog, "Message : " + STR(tnError, 5) + " " + tsMessage)
>	  = FPUTS(lhErrorLog, "Line    : " + STR(tnLine,  5) + " " + tsLine)
>	  = FPUTS(lhErrorLog, "Rechner : " + sys(0))
>	  = FPUTS(lhErrorLog, "*******************************************************" )
>	  = FPUTS(lhErrorLog, "")
>
>	* close
>	IF lhErrorLog >=0
>	  = FCLOSE(lhErrorLog)
>	ENDIF

>Now i want to delete the first 1000 lines from mylog.log when mylog.log has more then
>5000 lines.
>
>Can someone show me how to code this ??
>
>Best regards
>Albert