The FILE-CONTROL paragraph names each and every file and identifies the first medium through file control entries. The basic format of a file control entry is given below:
SELECT [OPTIONAL] file-name ASSIGN TO hardware-name.
In common, a COBOL source program uses some files. For each of these files, there should be a FILE-CONTROL entry. This entry names the file and assigns the peripheral device that holds that specific file. The file names which appear in the SELECT clauses should be exclusive and all these files should be described in DATA DIVISION. The file name must be formed according to the rules of data names.
The word OPTIONAL may be used only for the input files. Whenever the object program is executed, the optional files do not require being present on every juncture. If the optional clause is omitted for a specific file, the file should be present during the execution of the program. If the file is missing or absent, an execution error will occur. On the other hand, if an elective file is absent, any try to open the file for reading will not result in an error. But the absent file will be measured to be an empty file that means that the file does not contain any record.