Reading Physical Files in RPGLE with READ

Learning Objective

By the end of this lesson, you will be able to use READ in a loop to process every record in a physical file from beginning to end.

Simple Explanation

Once a database file is declared with dcl-f, as covered in the previous lesson, the RPGLE READ operation retrieves the next record from that file, one at a time, in whatever order the file naturally stores them, commonly arrival sequence for an unkeyed file. This is distinct from the read operation covered for display files, which waits for a user's response to a screen; here, READ retrieves the next stored record from a database file instead.

dcl-f CUSTMAST disk;

read CUSTMAST;
dow not %eof(CUSTMAST);
  dsply CUSTNAME;

  read CUSTMAST;
enddo;

*inlr = *on;

This loop follows the same shape as the READC loop covered in the Selecting a Row in a Subfile lesson: READ is called once before the loop starts, and again at the bottom of the loop, with %EOF, covered fully in the next lesson, checked as the loop's condition. Each pass through the loop processes one record retrieved from CUSTMAST, here simply displaying its customer name.

Why It Matters

READ is the most basic way an RPGLE program processes every record in a file, one at a time, which underlies many real business tasks: producing a report, checking every record for a condition, or performing the same action across an entire file. Understanding this loop shape is foundational to nearly all native RPGLE file processing.

Practical Example

Imagine a program that needs to display every customer's name in CUSTMAST. Using the loop shown above, the program reads the first customer record, displays its name, reads the next one, and continues until every record has been processed, at which point the loop ends naturally.

This is a simplified, illustrative example rather than a specific real program, but it reflects the essential, everyday shape of reading through an entire physical file in RPGLE.

Common Confusions

"Is this the same READ operation covered for display files?" No, though the operation name is the same. READ on a database file retrieves the next stored record from that file. read on a display file, covered in the READ, WRITE, EXFMT, and Screen Flow lesson, waits for a user's response to a screen already shown. The same operation name behaves differently depending on the kind of file it is used with.

"What order does READ retrieve records in?" For a file without a key, READ retrieves records in arrival sequence, the order they were originally stored, as covered in the Keyed Physical Files lesson. A keyed file can also be read this way, though CHAIN, covered in a later lesson, is used instead when looking up one specific record by key.

"Do I need the keyed keyword on dcl-f just to use READ this way?" No. Reading through a file from beginning to end with READ does not require keyed; keyed is specifically needed for CHAIN-based key lookups, covered later in this lesson group.

Quick Recap

• READ retrieves the next record from a database file, one at a time, commonly in arrival sequence for an unkeyed file.
• A basic read loop calls READ once before the loop and again at the bottom, the same shape used for READC with subfiles.
• READ on a database file is a different operation, despite the shared name, from read on a display file, which waits for user input instead.
• Reading through an entire file this way is foundational to many common RPGLE tasks, such as reports or full-file processing.

Try Asking the AI Tutor

Use the AI Tutor to ask follow-up questions about this lesson. For example, try asking:

• "What happens if I call READ on a file that has no records at all?"
• "Can I read a physical file in a specific field order without adding a key to it?"