LOCK limits or prevents access to a file by a network process.
UNLOCK releases the locks imposed by the last LOCK statement.
 
LOCK [#]filenumber% [,{record& | [start&] TO end&}]
UNLOCK [#]filenumber% [,{record& | [start&] TO end&}]
 
    - filenumber%        The number of an open file.
    - record&            For random-access files, the number of a record to
                         lock, relative to the first record in the file.
                         For binary files, the number of a byte to lock,
                         relative to the first byte in the file.
    - start& and end&    The numbers of the first and last records or bytes
                         in a range of records or bytes to lock or unlock.
 
    - For sequential files, LOCK and UNLOCK affect the entire file.
 
Example:
    'This example runs only in a network environment.
    OPEN "TEST.DAT" FOR RANDOM AS #1
    FOR i% = 1 TO 10
        PUT #1, , i%
    NEXT i%
    LOCK #1, 2         'Lock record 2.
    GET #1, 2, i%
    UNLOCK #1, 2       'Unlock record 2.