Concatenating files

For example, the following export command sets the MYFILE environment variable to STL-/home/myUserID/file1 followed by STL-/home/myUserID/file2:

export MYFILE='STL-/home/myUserID/file1:STL-/home/myUserID/file2'

The export command together with a SELECT and ASSIGN clause that associate the environment variable with a COBOL internal file-name causes the two files to be treated as a single file in the COBOL program:

SELECT concatfile ASSIGN TO MYFILE

Concatenation is supported if the assignment-name for the concatenation is an environment variable (as shown above), literal, or USING data-name.

A COBOL internal file assigned to a concatenation of file identifiers must meet the following criteria:

• ORGANIZATION is SEQUENTIAL or LINE SEQUENTIAL.
• ACCESS MODE is SEQUENTIAL.
• OPEN statements for the file have mode INPUT.

You can concatenate files that are in any of the file systems. You can specify the file-system ID for any or all of the file identifiers in a given concatenation. However, all file identifiers in a concatenation must specify or default at run time to the same file system, and all the files must have consistent attributes.

GDGs: You can concatenate entire generation data groups (GDGs) or individual generation files from one or more groups. If you specify a GDG in a concatenation, the most current generation file is read first, then the next most current, and so on until the least current generation file in the group is reached. It is an error to include a newly defined, and thus empty, GDG in a concatenation.

Validation of the individual file identifiers in a concatenation is deferred until the corresponding COBOL file is opened. At that time, the first identifier in the concatenation is resolved, and the open is attempted.

After a successful OPEN, the first file in the concatenation can be read until its last record has been reached. At the next READ statement, the next file identifier in the concatenation is resolved and opened.

If all the files in a concatenation are unavailable when an OPEN statement is executed for an optional COBOL file, the OPEN is successful and the file status key is set to 05. The first READ operation returns end-of-file, and the AT END condition exists.