COBOL Tutorial

COBOL FILE-ID Clause - Quick Reference

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Overview

The FILE-ID clause is used in file description entries (FD) to specify the external file identifier or name that the COBOL file will be associated with. This clause provides the essential link between the COBOL program's logical file definition and the actual external file in the operating system.

Purpose and Usage

File identification - Specify external file names
File association - Link COBOL files to external files
File access - Enable file operations
File naming - Provide meaningful file names
File organization - Support different file organizations

File Identification Concept

File Flow: [COBOL File] → [FILE-ID] → [External File] → [File Operations]

File Association: [FD Entry] → [FILE-ID Clause] → [Operating System File]

File Types: [Sequential] [Indexed] [Relative] [VSAM] [Database]

FILE-ID provides the bridge between COBOL and external files

FILE-ID enables COBOL programs to access external files through proper identification.

Syntax

The FILE-ID clause follows specific syntax patterns and is used within file description entries in the DATA DIVISION.

Basic Syntax

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* Basic FILE-ID clause syntax
FD file-name
    FILE-ID IS external-file-name.
    * File description content
 
* Examples
FD CUSTOMER-FILE
    FILE-ID IS "CUSTOMER.DAT".
    * Customer file description
 
FD TRANSACTION-FILE
    FILE-ID IS "TRANS.TXT".
    * Transaction file description
 
FD REPORT-FILE
    FILE-ID IS "REPORT.OUT".
    * Report file description
 
* Complete example with file description
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE ASSIGN TO "CUSTOMER.DAT".
 
DATA DIVISION.
FILE SECTION.
FD CUSTOMER-FILE
    FILE-ID IS "CUSTOMER.DAT"
    LABEL RECORDS ARE STANDARD
    RECORD CONTAINS 80 CHARACTERS
    DATA RECORD IS CUSTOMER-RECORD.
01 CUSTOMER-RECORD.
    05 CUSTOMER-ID PIC 9(5).
    05 CUSTOMER-NAME PIC X(30).
    05 CUSTOMER-ADDRESS PIC X(45).

FILE-ID is used in file description entries to specify external file names.

File ID Types

File ID Type	Description	Use Case
Literal file name	Direct file name specification	Fixed file names
Data name	Variable file name	Dynamic file names
Fully qualified path	Complete file path	Specific file locations
Logical file name	Logical file identifier	System file references
Environment variable	Environment-based file name	Portable file references

Usage in File Description

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* Using FILE-ID in file descriptions
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT INPUT-FILE ASSIGN TO "INPUT.DAT".
    SELECT OUTPUT-FILE ASSIGN TO "OUTPUT.DAT".
    SELECT REPORT-FILE ASSIGN TO "REPORT.TXT".
 
DATA DIVISION.
FILE SECTION.
FD INPUT-FILE
    FILE-ID IS "INPUT.DAT"
    LABEL RECORDS ARE STANDARD
    RECORD CONTAINS 100 CHARACTERS
    DATA RECORD IS INPUT-RECORD.
01 INPUT-RECORD.
    05 INPUT-DATA PIC X(100).
 
FD OUTPUT-FILE
    FILE-ID IS "OUTPUT.DAT"
    LABEL RECORDS ARE STANDARD
    RECORD CONTAINS 100 CHARACTERS
    DATA RECORD IS OUTPUT-RECORD.
01 OUTPUT-RECORD.
    05 OUTPUT-DATA PIC X(100).
 
FD REPORT-FILE
    FILE-ID IS "REPORT.TXT"
    LABEL RECORDS ARE OMITTED
    RECORD CONTAINS 132 CHARACTERS
    DATA RECORD IS REPORT-LINE.
01 REPORT-LINE.
    05 REPORT-TEXT PIC X(132).

FILE-ID is used within file description entries to specify external file names.

Common Use Cases

FILE-ID is commonly used in specific scenarios where file identification and access are needed.

Sequential File Processing

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* Sequential file processing with FILE-ID
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE ASSIGN TO "CUSTOMER.DAT".
 
DATA DIVISION.
FILE SECTION.
FD CUSTOMER-FILE
    FILE-ID IS "CUSTOMER.DAT"
    LABEL RECORDS ARE STANDARD
    RECORD CONTAINS 80 CHARACTERS
    DATA RECORD IS CUSTOMER-RECORD.
01 CUSTOMER-RECORD.
    05 CUSTOMER-ID PIC 9(5).
    05 CUSTOMER-NAME PIC X(30).
    05 CUSTOMER-ADDRESS PIC X(45).
 
WORKING-STORAGE SECTION.
01 END-OF-FILE PIC X VALUE 'N'.
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    OPEN INPUT CUSTOMER-FILE
    READ CUSTOMER-FILE
        AT END MOVE 'Y' TO END-OF-FILE
    END-READ
    
    PERFORM UNTIL END-OF-FILE = 'Y'
        DISPLAY "Customer: " CUSTOMER-NAME
        READ CUSTOMER-FILE
            AT END MOVE 'Y' TO END-OF-FILE
        END-READ
    END-PERFORM
    
    CLOSE CUSTOMER-FILE
    STOP RUN.

Use FILE-ID for sequential file processing with proper file identification.

Indexed File Operations

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* Indexed file operations with FILE-ID
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT EMPLOYEE-FILE ASSIGN TO "EMPLOYEE.IDX"
        ORGANIZATION IS INDEXED
        ACCESS MODE IS RANDOM
        RECORD KEY IS EMPLOYEE-ID.
 
DATA DIVISION.
FILE SECTION.
FD EMPLOYEE-FILE
    FILE-ID IS "EMPLOYEE.IDX"
    LABEL RECORDS ARE STANDARD
    RECORD CONTAINS 100 CHARACTERS
    DATA RECORD IS EMPLOYEE-RECORD.
01 EMPLOYEE-RECORD.
    05 EMPLOYEE-ID PIC 9(5).
    05 EMPLOYEE-NAME PIC X(30).
    05 EMPLOYEE-DEPARTMENT PIC X(20).
    05 EMPLOYEE-SALARY PIC 9(8)V99.
    05 FILLER PIC X(35).
 
WORKING-STORAGE SECTION.
01 SEARCH-ID PIC 9(5).
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    OPEN INPUT EMPLOYEE-FILE
    MOVE 10001 TO SEARCH-ID
    
    READ EMPLOYEE-FILE
        INVALID KEY DISPLAY "Employee not found"
        NOT INVALID KEY DISPLAY "Employee: " EMPLOYEE-NAME
    END-READ
    
    CLOSE EMPLOYEE-FILE
    STOP RUN.

Use FILE-ID for indexed file operations with proper file identification.

Report File Generation

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* Report file generation with FILE-ID
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT SALES-FILE ASSIGN TO "SALES.DAT".
    SELECT REPORT-FILE ASSIGN TO "SALES.RPT".
 
DATA DIVISION.
FILE SECTION.
FD SALES-FILE
    FILE-ID IS "SALES.DAT"
    LABEL RECORDS ARE STANDARD
    RECORD CONTAINS 50 CHARACTERS
    DATA RECORD IS SALES-RECORD.
01 SALES-RECORD.
    05 PRODUCT-ID PIC 9(5).
    05 PRODUCT-NAME PIC X(20).
    05 SALES-AMOUNT PIC 9(8)V99.
    05 FILLER PIC X(17).
 
FD REPORT-FILE
    FILE-ID IS "SALES.RPT"
    LABEL RECORDS ARE OMITTED
    RECORD CONTAINS 132 CHARACTERS
    DATA RECORD IS REPORT-LINE.
01 REPORT-LINE.
    05 REPORT-TEXT PIC X(132).
 
WORKING-STORAGE SECTION.
01 END-OF-FILE PIC X VALUE 'N'.
01 TOTAL-SALES PIC 9(10)V99 VALUE ZERO.
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    OPEN INPUT SALES-FILE
    OPEN OUTPUT REPORT-FILE
    
    * Write report header
    MOVE "SALES REPORT" TO REPORT-TEXT
    WRITE REPORT-LINE
    
    READ SALES-FILE
        AT END MOVE 'Y' TO END-OF-FILE
    END-READ
    
    PERFORM UNTIL END-OF-FILE = 'Y'
        ADD SALES-AMOUNT TO TOTAL-SALES
        MOVE SALES-RECORD TO REPORT-TEXT
        WRITE REPORT-LINE
        READ SALES-FILE
            AT END MOVE 'Y' TO END-OF-FILE
        END-READ
    END-PERFORM
    
    * Write total
    MOVE "TOTAL SALES: " TO REPORT-TEXT(1:13)
    MOVE TOTAL-SALES TO REPORT-TEXT(14:12)
    WRITE REPORT-LINE
    
    CLOSE SALES-FILE REPORT-FILE
    STOP RUN.

Use FILE-ID for report file generation with proper file identification.

Best Practices and Tips

Following these best practices ensures effective use of the FILE-ID clause for proper file handling.

FILE-ID Design Principles

Use meaningful names - Choose descriptive file names
Follow naming conventions - Use consistent file naming patterns
Consider portability - Use portable file name formats
Validate file existence - Check if files exist before use
Handle file errors - Implement proper error handling
Document file purposes - Document what each file contains

Common Pitfalls to Avoid

Pitfall	Problem	Solution
Hard-coded file names	Poor portability and maintenance	Use configuration files or parameters
Missing file validation	Runtime errors when files don't exist	Always validate file existence
Inconsistent naming	Confusing and hard to maintain	Use consistent naming conventions
No error handling	Program crashes on file errors	Implement proper error handling
Platform-specific paths	Poor cross-platform compatibility	Use portable path formats

Performance Considerations

File access patterns - Consider how files will be accessed
File organization - Choose appropriate file organization
Buffer management - Optimize buffer sizes for performance
File sharing - Consider file sharing requirements
Disk I/O optimization - Minimize disk I/O operations
File locking - Handle file locking appropriately

When to Use FILE-ID

Use Case	FILE-ID Suitability	Reasoning
File processing	Essential	Required for all file operations
Data input/output	Essential	Necessary for file I/O operations
Report generation	Essential	Required for output file creation
Memory-only programs	Not applicable	No file operations needed
Database-only programs	Poor	Use database connections instead

FILE-ID Clause Quick Reference

Usage	Syntax	Example
Basic file ID	FILE-ID IS file-name	FILE-ID IS "DATA.DAT"
Variable file ID	FILE-ID IS data-name	FILE-ID IS FILE-NAME-VAR
Full path file ID	FILE-ID IS "path/file"	FILE-ID IS "/usr/data/file.txt"
Logical file ID	FILE-ID IS logical-name	FILE-ID IS "SYSIN"
Environment file ID	FILE-ID IS env-var	FILE-ID IS "$DATA_FILE"

Test Your Knowledge

1. What is the primary purpose of the FILE-ID clause in COBOL?

To define data types
To specify the external file identifier or name for a file
To control file operations
To perform calculations

2. Where is the FILE-ID clause typically used?

In DATA DIVISION
In file description entries (FD) in the DATA DIVISION
In PROCEDURE DIVISION
In ENVIRONMENT DIVISION

3. What is the main benefit of using FILE-ID?

Faster execution
Associates COBOL files with external file names and enables file access
Memory optimization
Simpler syntax

4. When is the FILE-ID clause most useful?

In programs without files
In programs that need to access external files
Only during compilation
Only during program termination

5. How does FILE-ID relate to file operations?

They are completely independent
FILE-ID is essential for enabling file operations by linking to external files
FILE-ID overrides file operation features
They serve the same purpose

COBOL Tutorial

COBOL FILE-ID Clause - Quick Reference

Overview

Purpose and Usage

File Identification Concept

Syntax

Basic Syntax

File ID Types

Usage in File Description

Common Use Cases

Sequential File Processing

Indexed File Operations

Report File Generation

Best Practices and Tips

FILE-ID Design Principles

Common Pitfalls to Avoid

Performance Considerations

When to Use FILE-ID

FILE-ID Clause Quick Reference

Test Your Knowledge

Frequently Asked Questions

Related Concepts

ASSIGN Clause

SELECT Statement

File Description Entries

File Processing

File Organization

Related Pages

COBOL Tutorial

COBOL FILE-ID Clause - Quick Reference

Overview

Purpose and Usage

File Identification Concept

Syntax

Basic Syntax

File ID Types

Usage in File Description

Common Use Cases

Sequential File Processing

Indexed File Operations

Report File Generation

Best Practices and Tips

FILE-ID Design Principles

Common Pitfalls to Avoid

Performance Considerations

When to Use FILE-ID

FILE-ID Clause Quick Reference

Test Your Knowledge

Frequently Asked Questions

What is the difference between FILE-ID and ASSIGN clause?

Can FILE-ID be used without ASSIGN clause?

What types of file names can be specified in FILE-ID?

How do you specify a FILE-ID in COBOL?

Are there any restrictions on FILE-ID values?

Related Concepts

ASSIGN Clause

SELECT Statement

File Description Entries

File Processing

File Organization

Related Pages