Updated: 11 December 1998

OpenVMS User's Manual

Chapter 14
14	Programming with DCL: Defining Symbols, Commands, and Expressions
14.1	About Symbols
14.1.1	Comparing Logical Names and Symbols
14.2	Using Symbols
14.2.1	Using Symbols to Represent DCL Commands
14.2.2	Symbol Abbreviation
14.2.3	Defining Foreign Commands
14.2.4	Symbol Substitution
14.2.5	Deleting Symbols
14.3	Displaying Symbols
14.4	Using Symbols with Other Symbols
14.4.1	Symbol Concatenation
14.4.2	Including Symbols in String Assignments
14.5	Using Symbols to Store and Manipulate Data
14.6	Character Strings
14.6.1	Defining Character Strings
14.6.2	Character String Expressions
14.6.3	Character String Operations
14.6.4	Comparing Character Strings
14.6.5	Replacing Substrings
14.7	Using Numeric Values and Expressions
14.7.1	Specifying Numbers
14.7.2	Internal Storage of Numbers
14.7.3	Performing Arithmetic Operations
14.7.4	Comparing Numbers
14.7.5	Performing Numeric Overlays
14.8	Using Logical Values and Expressions
14.8.1	Logical Operations
14.8.2	Logical Expressions
14.8.3	Logical Operation Results
14.8.4	Using Values Returned by Lexical Functions
14.8.5	Order of Operations
14.8.6	Evaluating Data Types
14.9	Converting Value Types in Expressions
14.9.1	Converting Strings to Integers
14.9.2	Converting Integers to Strings
14.10	Understanding Symbol Tables
14.10.1	Local Symbol Tables
14.10.2	Global Symbol Tables
14.10.3	Symbol Table Search Order
14.11	Masking the Value of Symbols
14.11.1	SET SYMBOL Command
14.11.2	Symbol Scoping State
14.12	Understanding Symbol Substitution
14.12.1	Forced Symbol Substitution
14.12.2	Symbol Substitution Operators
14.13	The Three Phases of Command Processing
14.13.1	Phase 1: Command Input Scanning
14.13.2	Phase 2: Command Parsing
14.13.3	Phase 3: Expression Evaluation
14.13.4	Repetitive and Iterative Substitution
14.13.5	Undefined Symbols
14.14	An Alternative to Using Symbols: Automatic Foreign Commands
14.14.1	Using Automatic Foreign Commands
14.14.2	Automatic Foreign Command Restrictions
Chapter 15
15	Programming with DCL: Introduction to Command Procedures
15.1	Basic Information for Writing Command Procedures
15.1.1	Default File Type
15.1.2	Writing Commands
15.1.3	Writing Command Lines
15.2	Using Labels in Command Lines
15.2.1	Labels in Local Symbol Tables
15.2.2	Duplicate Labels
15.3	Using Comments in Command Procedures
15.4	How to Write Command Procedures
15.5	Steps for Writing Command Procedures
15.5.1	Step 1: Design the Command Procedure
15.5.2	Step 2: Assign Variables and Test Conditionals
15.5.2.1	Using the INQUIRE Command
15.5.2.2	Preserving Literal Characters
15.5.2.3	Testing Conditionals Using IF and THEN
15.5.2.4	Writing Program Stubs
15.5.3	Step 3: Add Loops
15.5.4	Step 4: End the Command Procedure
15.5.4.1	Using the EXIT Command
15.5.4.2	Using the STOP Command
15.5.5	Step 5: Test and Debug the Program Logic
15.5.5.1	Debugging Command Procedures
15.5.5.2	Enabling Verification During Execution
15.5.6	Step 6: Add Cleanup Tasks
15.5.6.1	Closing Files
15.5.6.2	Deleting Temporary or Extraneous Files
15.5.6.3	Commonly Changed Process Characteristics
15.5.6.4	Ensuring Cleanup Operations Are Performed
15.5.7	Step 7: Complete the Command Procedure
15.6	Executing Command Procedures
15.6.1	Executing Command Procedures from Within Other Command Procedures
15.6.2	Executing Command Procedures on Remote Nodes
15.6.2.1	Security Note
15.6.3	Executing Command Procedures with DCL Qualifiers or Parameters
15.6.3.1	Restrictions
15.6.4	Executing Command Procedures Interactively
15.6.5	Executing Command Procedures as Batch Jobs
15.6.5.1	Remote Batch Jobs
15.6.5.2	Restarting Batch Jobs
15.6.6	Executing Command Procedures on Disk and Tape Volumes
15.6.6.1	Executing on Private Disk Volumes
15.6.6.2	Executing on Tape Volumes
15.7	Exiting and Interrupting Command Procedures
15.7.1	Methods of Exiting
15.7.2	Exit-Handling Routines
15.8	Handling Errors
15.8.1	Default Error Actions
15.9	Other Methods of Error Handling
15.9.1	ON Command
15.10	Using the SET NOON Command
15.11	Handling Ctrl/Y Interruptions
15.11.1	Stopping Command Procedures
15.11.2	Stopping Privileged Images
15.12	Setting Ctrl/Y Action Routines
15.12.1	Using the ON Command
15.12.2	Effects of Entering Ctrl/Y
15.13	Disabling and Enabling Ctrl/Y Interruptions
15.13.1	Using SET NOCONTROL=Y
15.13.2	Using SET CONTROL=Y
15.14	Detecting Errors in Command Procedures Using Condition Codes
15.14.1	Displaying Condition Codes ($STATUS)
15.14.2	Condition Codes with the EXIT Command
15.14.3	Determining Severity Levels
15.14.4	Testing for Successful Completion
15.15	Using Commands That Do Not Set $STATUS
15.16	Login Command Procedures
15.16.1	Systemwide Login Command Procedures
15.16.2	Personal Login Command Procedures
15.16.3	Login Command Procedures in Captive Accounts

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