After the execution of any file I/O verb (CLOSE, DELETE, OPEN, READ, REWRITE, START, UNLOCK, or WRITE), information about the I/O is available in the form of a status number. This number is placed in the FILE STATUS variable for the appropriate file if one has been declared.
Status-variable must be the name of an alphanumeric Working-Storage or Linkage data item with a size of 2 characters. The first digit indicates a general classification of the status, while the second digit provides detail information. Any file status whose first digit is '0' is considered a successful I/O. Any non-zero initial digit indicates failure.
Appendix J, Book 4, "Appendices" covers the exact values returned for each I/O condition.