proc main
   string sLine                           ;Line of data read from/written to open file
   string sPrevLine                       ;Previous line of data from file
   integer iLen                           ;Holds length of sLine
   long lLen                              ;Long variable used in disk operations

   if fopen 0 "test.txt" READWRITE        ;If file is opened successfully
      while not feof 0                    ;While data exists...
         fgets 0 sLine                    ;Read line from file
         if not strcmp sLine sPrevLine    ;If data is not identical to previous line
            sPrevLine = sLine             ;Then save current data for next compare
         else
            strlen sLine iLen             ;Get length of line
            lLen = iLen                   ;Save in long variable for use in disk operations
            fseek 0 (-lLen) 1             ;Back up file pointer by length of current line
            fdelblock 0 iLen              ;Delete current line
            ftell 0 lLen                  ;Get current file pointer
            fclose 0                      ;Close file
            fopen 0 "test.txt" READWRITE  ;Reopen file so we can continue checking the remainder
            fseek 0 lLen 0                ;Set file pointer to previously-read location
         endif
      endwhile
      fclose 0                            ;Close file
   endif
endproc