In this module, we will delve into advanced file operations in Control Language (CL). This topic is crucial for managing complex file-related tasks efficiently. We will cover advanced commands and techniques that go beyond basic file management.

1. File Attributes and Metadata: Understanding and manipulating file attributes.
2. File Locking Mechanisms: Ensuring data integrity during concurrent access.
3. Advanced File I/O Operations: Performing complex read/write operations.
4. File Triggers: Automating actions based on file events.

File attributes provide essential information about a file, such as its size, type, and permissions. In CL, you can use commands to view and modify these attributes.

• DSPFD (Display File Description): Displays detailed information about a file.
• CHGATR (Change Attribute): Changes the attributes of a file.

Example: Displaying File Description

This command displays the description of the file MYFILE in the library MYLIB.

Example: Changing File Attribute

This command changes the attribute of MYFILE to disallow updates.

File locking is essential to prevent data corruption when multiple processes access the same file simultaneously.

• Exclusive Lock: Only one process can access the file.
• Shared Lock: Multiple processes can read the file, but no process can write to it.

• ALCOBJ (Allocate Object): Allocates an object to a job, effectively locking it.
• DLCOBJ (Deallocate Object): Deallocates an object, releasing the lock.

Example: Allocating an Object

This command allocates MYFILE with an exclusive lock.

Example: Deallocating an Object

This command deallocates MYFILE, releasing the exclusive lock.

Advanced file I/O operations involve more complex read and write tasks, such as handling large files or performing batch updates.

• CPYF (Copy File): Copies records from one file to another.
• RGZPFM (Reorganize Physical File Member): Reorganizes a physical file member to reclaim space.

Example: Copying File with Conditions

This command copies records from SRCFILE to DSTFILE, creating the destination file if it does not exist and including only records with a length of 80 characters.

Example: Reorganizing a File

This command reorganizes MYFILE to reclaim unused space.

File triggers allow you to automate actions based on specific file events, such as record insertions, updates, or deletions.

• ADDPFTRG (Add Physical File Trigger): Adds a trigger to a physical file.
• RMVPFTRG (Remove Physical File Trigger): Removes a trigger from a physical file.

Example: Adding a Trigger

This command adds a trigger to MYFILE that calls the program MYPGM after a record is inserted.

Example: Removing a Trigger

This command removes the trigger from MYFILE that was set to activate after a record insertion.

1. Display the attributes of a file named TESTFILE in the library TESTLIB.
2. Change the attribute to disallow updates.

Solution

1. Allocate the file TESTFILE with an exclusive lock.
2. Deallocate the file.

Solution

1. Copy records from SRCFILE to DSTFILE in the library TESTLIB, including only records with a length of 100 characters.

Solution

1. Add a trigger to TESTFILE that calls the program TRGPGM after a record is inserted.
2. Remove the trigger.

Solution

In this module, we covered advanced file operations in CL, including manipulating file attributes, implementing file locking mechanisms, performing advanced file I/O operations, and setting up file triggers. These skills are essential for managing complex file-related tasks efficiently and ensuring data integrity in multi-user environments.

Next, we will explore advanced job scheduling techniques in the following module.