When WRITE is used to write data to an internal file, the following specifiers are associated with the statement:
UNIT=<value>
<value> specifies the unit number. The keyword and equals sign are
optional if it is the first item in the list.
FMT=<string, label or *>
Specifies the format for the data to be written. The keyword and equals sign
are optional if it is the second item in the list.
IOSTAT=<variable>
<variable> will contain zero if the operation was successful, otherwise a
positive value to indicate an error, -1 to indicate EOF or -2 to indicate EOR.
ERR=<label>
<label> specifies a label to go to in the event of an error.