LOCK                     Control File or Record Access

 LOCK [#] filenum [,{record | [start] TO end}]
 .
 . [statements]
 .
 UNLOCK [#] filenum [,{record | [start] TO end}]

    Make a specified record range or an entire file inaccessible to other
    users.

     filenum    The number under which the file was OPENed.

      record    The number of a record to be LOCKed or UNLOCKed.

       start    The number of the first record to be LOCKed or UNLOCKed.

         end    The number of the last record to be LOCKed or UNLOCKed.

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      Notes:    If the file specified by filenum has been opened for
                random access, you may lock either a single record number
                (with the record argument) or a range of record numbers.
                If you specify a range and omit the start argument, all
                records from the beginning of the file to end are locked.

                If the file specified by filenum was opened for sequential
                input or output, the entire file is locked.

                LOCK requires DOS 3.0 or later and SHARE.EXE.

                It is important to UNLOCK all LOCKed records before
                closing the file.