COBOL Tutorial

COBOL ENTER Statement

The ENTER statement represents a specialized component of language integration and external system interface operations in COBOL, serving as a mechanism for invoking external programs, system services, or alternative language environments. This statement embodies modern integration principles by providing structured interfaces for external program calls, enabling sophisticated system integration capabilities, and supporting the development of hybrid applications that require precise control over external program invocation and inter-language communication procedures.

Understanding ENTER Statement

The ENTER statement is an obsolete COBOL feature that was originally designed to allow COBOL programs to interface with programs written in other languages or to invoke system-specific operations. In modern COBOL implementations, this functionality has been largely replaced by more standardized mechanisms such as the CALL statement and system-specific APIs.

While ENTER is rarely used in contemporary COBOL development, understanding its historical context and purpose is important for maintaining legacy systems and understanding the evolution of COBOL's integration capabilities. Modern alternatives provide better portability, error handling, and standardization across different COBOL implementations.

Historical ENTER Usage

cobol

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
IDENTIFICATION DIVISION.
PROGRAM-ID. ENTER-DEMO.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  INTEGRATION-CONTROLS.
    05  EXTERNAL-CALL-COUNT     PIC 9(5) VALUE 0.
    05  SUCCESSFUL-CALLS        PIC 9(5) VALUE 0.
    05  FAILED-CALLS            PIC 9(3) VALUE 0.
    05  CALL-STATUS             PIC X VALUE 'N'.
        88  CALL-SUCCESS        VALUE 'Y'.
        88  CALL-FAILED         VALUE 'N'.
 
01  SYSTEM-INTERFACE.
    05  SYSTEM-COMMAND          PIC X(100).
    05  RETURN-CODE             PIC 9(3) VALUE 0.
    05  ERROR-MESSAGE           PIC X(80).
 
01  LEGACY-PARAMETERS.
    05  LANGUAGE-NAME           PIC X(10) VALUE 'ASSEMBLER'.
    05  ROUTINE-NAME            PIC X(20) VALUE 'SYSROUTINE'.
    05  PARAMETER-BLOCK         PIC X(256).
 
PROCEDURE DIVISION.
MAIN-PROCESSING.
    PERFORM DEMONSTRATE-LEGACY-ENTER-CONCEPT
    PERFORM DEMONSTRATE-MODERN-ALTERNATIVES
    PERFORM DISPLAY-INTEGRATION-STATISTICS
    STOP RUN.
 
DEMONSTRATE-LEGACY-ENTER-CONCEPT.
    DISPLAY 'Demonstrating legacy ENTER concept...'
    
    *> Historical ENTER statement usage (obsolete)
    *> ENTER language-name routine-name parameters
    *> This syntax is no longer supported in modern COBOL
    
    DISPLAY 'Note: ENTER statement is obsolete in modern COBOL'
    DISPLAY 'Historical syntax was:'
    DISPLAY 'ENTER ' LANGUAGE-NAME ' ' ROUTINE-NAME
    
    *> Simulate the concept for educational purposes
    MOVE 'ASSEMBLER' TO LANGUAGE-NAME
    MOVE 'MATH-ROUTINE' TO ROUTINE-NAME
    
    DISPLAY 'Would have called: ' LANGUAGE-NAME ' routine: ' ROUTINE-NAME
    
    ADD 1 TO EXTERNAL-CALL-COUNT
    SET CALL-SUCCESS TO TRUE
    ADD 1 TO SUCCESSFUL-CALLS.
 
DEMONSTRATE-MODERN-ALTERNATIVES.
    DISPLAY 'Demonstrating modern alternatives to ENTER...'
    
    *> Modern CALL statement usage
    PERFORM DEMONSTRATE-CALL-STATEMENT
    PERFORM DEMONSTRATE-SYSTEM-INTERFACE
    PERFORM DEMONSTRATE-FUNCTION-CALLS
    
    DISPLAY 'Modern alternatives demonstrated'.
 
DEMONSTRATE-CALL-STATEMENT.
    DISPLAY 'Using modern CALL statement...'
    
    *> Modern equivalent using CALL
    CALL 'EXTERNAL-ROUTINE' USING PARAMETER-BLOCK
        ON EXCEPTION
            DISPLAY 'External routine call failed'
            SET CALL-FAILED TO TRUE
            ADD 1 TO FAILED-CALLS
        NOT ON EXCEPTION
            DISPLAY 'External routine call successful'
            SET CALL-SUCCESS TO TRUE
            ADD 1 TO SUCCESSFUL-CALLS
    END-CALL
    
    ADD 1 TO EXTERNAL-CALL-COUNT.
 
DEMONSTRATE-SYSTEM-INTERFACE.
    DISPLAY 'Using system interface calls...'
    
    *> System command execution
    MOVE 'DIR' TO SYSTEM-COMMAND  *> Windows example
    
    CALL 'SYSTEM' USING SYSTEM-COMMAND
        RETURNING RETURN-CODE
        ON EXCEPTION
            DISPLAY 'System command failed'
            MOVE 'System call exception' TO ERROR-MESSAGE
            SET CALL-FAILED TO TRUE
            ADD 1 TO FAILED-CALLS
        NOT ON EXCEPTION
            DISPLAY 'System command executed'
            DISPLAY 'Return code: ' RETURN-CODE
            SET CALL-SUCCESS TO TRUE
            ADD 1 TO SUCCESSFUL-CALLS
    END-CALL
    
    ADD 1 TO EXTERNAL-CALL-COUNT.
 
DEMONSTRATE-FUNCTION-CALLS.
    DISPLAY 'Using intrinsic functions...'
    
    *> Modern intrinsic function usage
    DISPLAY 'Current date: ' FUNCTION CURRENT-DATE
    DISPLAY 'Random number: ' FUNCTION RANDOM(123)
    DISPLAY 'Length of string: ' FUNCTION LENGTH('HELLO WORLD')
    
    *> These are built-in and don't require external calls
    SET CALL-SUCCESS TO TRUE
    ADD 1 TO SUCCESSFUL-CALLS
    ADD 1 TO EXTERNAL-CALL-COUNT.
 
DISPLAY-INTEGRATION-STATISTICS.
    DISPLAY 'Integration Statistics:'
    DISPLAY 'Total external calls: ' EXTERNAL-CALL-COUNT
    DISPLAY 'Successful calls: ' SUCCESSFUL-CALLS
    DISPLAY 'Failed calls: ' FAILED-CALLS
    
    IF EXTERNAL-CALL-COUNT > 0
        COMPUTE SUCCESSFUL-CALLS = 
            (SUCCESSFUL-CALLS / EXTERNAL-CALL-COUNT) * 100
        DISPLAY 'Success rate: ' SUCCESSFUL-CALLS '%'
    END-IF
    
    DISPLAY ''
    DISPLAY 'Modern COBOL Integration Recommendations:'
    DISPLAY '1. Use CALL statement for external programs'
    DISPLAY '2. Use intrinsic functions for built-in operations'
    DISPLAY '3. Use system APIs for OS-specific operations'
    DISPLAY '4. Consider web services for modern integration'
    DISPLAY '5. Use JSON/XML for data interchange'.

Modern Integration Alternatives

cobol

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
IDENTIFICATION DIVISION.
PROGRAM-ID. MODERN-INTEGRATION.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  MODERN-INTEGRATION-EXAMPLES.
    05  WEB-SERVICE-URL         PIC X(200).
    05  JSON-REQUEST            PIC X(1000).
    05  JSON-RESPONSE           PIC X(2000).
    05  HTTP-STATUS             PIC 9(3).
 
01  DATABASE-INTEGRATION.
    05  SQL-STATEMENT           PIC X(500).
    05  CONNECTION-STRING       PIC X(200).
    05  RESULT-SET-COUNT        PIC 9(7).
 
01  FILE-SYSTEM-OPERATIONS.
    05  FILE-PATH               PIC X(100).
    05  OPERATION-TYPE          PIC X(10).
    05  FILE-SIZE               PIC 9(9).
 
PROCEDURE DIVISION.
MAIN-PROCESSING.
    PERFORM DEMONSTRATE-WEB-SERVICE-INTEGRATION
    PERFORM DEMONSTRATE-DATABASE-INTEGRATION
    PERFORM DEMONSTRATE-FILE-SYSTEM-OPERATIONS
    STOP RUN.
 
DEMONSTRATE-WEB-SERVICE-INTEGRATION.
    DISPLAY 'Modern web service integration...'
    
    MOVE 'https://api.example.com/data' TO WEB-SERVICE-URL
    MOVE '{"request":"data","format":"json"}' TO JSON-REQUEST
    
    *> Modern web service call (conceptual)
    CALL 'HTTP-CLIENT' USING 
        WEB-SERVICE-URL
        JSON-REQUEST
        JSON-RESPONSE
        HTTP-STATUS
    END-CALL
    
    IF HTTP-STATUS = 200
        DISPLAY 'Web service call successful'
        DISPLAY 'Response: ' JSON-RESPONSE(1:100)
    ELSE
        DISPLAY 'Web service call failed: ' HTTP-STATUS
    END-IF.
 
DEMONSTRATE-DATABASE-INTEGRATION.
    DISPLAY 'Modern database integration...'
    
    MOVE 'SELECT * FROM CUSTOMERS WHERE STATUS = ACTIVE' TO SQL-STATEMENT
    MOVE 'DRIVER=SQL Server;SERVER=localhost;DATABASE=mydb' TO CONNECTION-STRING
    
    *> Modern database call (conceptual)
    EXEC SQL
        CONNECT TO :CONNECTION-STRING
    END-EXEC
    
    EXEC SQL
        EXECUTE IMMEDIATE :SQL-STATEMENT
    END-EXEC
    
    EXEC SQL
        GET DIAGNOSTICS :RESULT-SET-COUNT = ROW_COUNT
    END-EXEC
    
    DISPLAY 'Database query executed'
    DISPLAY 'Rows affected: ' RESULT-SET-COUNT.
 
DEMONSTRATE-FILE-SYSTEM-OPERATIONS.
    DISPLAY 'Modern file system operations...'
    
    MOVE 'C:DATAINPUT.TXT' TO FILE-PATH
    MOVE 'READ' TO OPERATION-TYPE
    
    *> Modern file system API call (conceptual)
    CALL 'FILE-SYSTEM-API' USING
        FILE-PATH
        OPERATION-TYPE
        FILE-SIZE
    END-CALL
    
    DISPLAY 'File operation completed'
    DISPLAY 'File path: ' FILE-PATH
    DISPLAY 'File size: ' FILE-SIZE ' bytes'.

Best Practices and FAQ

Modern Alternatives

• Use CALL statement for external programs
• Use intrinsic functions for built-in operations
• Use EXEC SQL for database operations
• Use web services for modern integration
• Use JSON/XML for data interchange

Legacy Considerations

• ENTER is obsolete in modern COBOL
• Replace with standardized alternatives
• Improve error handling capabilities
• Enhance portability across platforms
• Use modern integration patterns

COBOL Tutorial

COBOL ENTER Statement

Understanding ENTER Statement

Historical ENTER Usage

Modern Integration Alternatives

Best Practices and FAQ

Why is ENTER obsolete in modern COBOL?

What should I use instead of ENTER?

How do I modernize legacy ENTER statements?