The CLOSE statement is used to disconnect a file which has been connected with
OPEN. It has the following specifiers associated with it:
<value> is the unit number. The keyword and equals sign are optional if
this is the first specifier in the list.
<variable> specifies an integer variable into which the input/output
status will be written. A positive value will be written on error, zero
<label> specifies a label to jump to in the event of an error.
<string> is either 'KEEP' or 'DELETE'. The default for named files is
'KEEP', for scratch files is 'DELETE'.