COMMAND Statement

Purpose

The COMMAND statement (abbreviated as CMD) allows batch jobs to issue MVS system commands, JES2 commands, or JES3 commands during job execution. This provides a way to automate operator actions that would otherwise require manual intervention, such as mounting tapes, starting processes, modifying system parameters, or displaying system status.

Key Benefit:

The COMMAND statement enables automation of operator tasks directly from JCL, reducing the need for manual intervention during batch job execution and allowing jobs to interact with the operating system environment.

Basic Syntax

Simple Format

jcl

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//         COMMAND 'system-command'
// or
//         CMD 'system-command'

The command must be enclosed in single quotes and can be any valid MVS, JES2, or JES3 command.

Syntax Variants

jcl

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//         COMMAND PREFIX=xx 'system-command'
//         COMMAND REL=JES3 'system-command'
//         COMMAND REL=JES2 'system-command'
//         COMMAND REL=SYSTEM 'system-command'

Command Timing

Placement	Execution Timing
Before first EXEC	Executed when the job is selected for execution
Between job steps	Executed after the previous step completes and before the next step begins
After last step	Executed after the last step completes, during job termination

Parameters

Parameter	Description
`PREFIX=xx`	Specifies a prefix to be used with the command (e.g., PREFIX=$)
`REL=SYSTEM`	Indicates that the command is an MVS system command
`REL=JES2`	Indicates that the command is a JES2 command
`REL=JES3`	Indicates that the command is a JES3 command

Usage Examples

Display System Information

jcl

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//SYSINF   JOB (ACCT#),'OPERATOR',CLASS=A
//         COMMAND 'D A,L'             /* Display active jobs */
//STEP1    EXEC PGM=IEFBR14
//         COMMAND 'D T'               /* Display time and date */

This job displays a list of active jobs before executing STEP1, then displays the current time and date after STEP1 completes.

Modify System Resources

jcl

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//MODRES   JOB (ACCT#),'OPERATOR',CLASS=A
//         COMMAND 'S CICSRGN'         /* Start CICS region */
//STEP1    EXEC PGM=CICSPROC
//         COMMAND 'F CICSRGN,CEMT PERFORM STATISTICS'
//STEP2    EXEC PGM=CLEANUP
//         COMMAND 'P CICSRGN'         /* Stop CICS region */

This job starts a CICS region, performs a process, requests statistics, and then stops the CICS region, all automated within JCL.

Control JES Resources

jcl

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//JESCTL   JOB (ACCT#),'OPERATOR',CLASS=A
//         COMMAND REL=JES2 '$P PRT1'   /* Pause printer 1 */
//STEP1    EXEC PGM=PRTMAINT
//         COMMAND REL=JES2 '$T PRT1,F=STD3'  /* Change form */
//         COMMAND REL=JES2 '$S PRT1'   /* Start printer 1 */

This job controls a JES2 printer by pausing it, executing maintenance, changing the form type, and then restarting the printer.

Dynamic Allocation Control

jcl

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//DEVCTL   JOB (ACCT#),'OPERATOR',CLASS=A
//         COMMAND 'MOUNT TAPE01,VOL=123456,UNIT=TAPE'
//STEP1    EXEC PGM=TAPEDUMP
//         COMMAND 'UNLOAD TAPE01'
//STEP2    EXEC PGM=REPORT

This job issues commands to mount a tape before processing and unload it afterward, automating tape handling operations.

Security Considerations

Authorization Required: Jobs that use COMMAND statements typically need special authorization
Restricted Commands: Some commands may be disallowed or restricted based on security settings
Command Validation: Security products like RACF, ACF2, or Top Secret validate command permissions
Audit Logging: Commands issued via JCL are typically logged for security audit purposes
Potential Impact: Commands can affect system-wide resources, so proper controls are essential

Security Configuration

Security for COMMAND statements is typically controlled through:

RACF OPERCMDS class profiles
ACF2 command limiting controls
Top Secret command authorization settings
Installation-specific command exits

Common Use Cases

Application Environment Setup: Starting or configuring application regions before processing
Resource Management: Allocating or freeing system resources dynamically during job execution
Automated Operations: Performing operator tasks without manual intervention
Status Monitoring: Displaying system information at specific points in the job
Scheduled Maintenance: Performing system maintenance activities during batch windows
Disaster Recovery: Issuing commands to configure resources during recovery scenarios

Best Practices

Use Comments to document the purpose of each command
Specify REL= parameter explicitly for clarity and to avoid ambiguity
Plan for command failure by including error handling in the job
Use descriptive jobnames for jobs containing system commands
Consider security implications of every command issued
Limit command usage to necessary operations only
Test commands thoroughly in non-production environments
Document command dependencies between jobs and systems

Limitations

Command Length: Limited to approximately 124 characters
Response Processing: Command responses appear in the system log, not the job log
Error Handling: Limited ability to detect and respond to command failures
Timing Considerations: No guarantee of precise timing when commands are executed
Conditional Execution: Cannot conditionally issue commands based on command responses
Security Restrictions: May be limited by installation security policies

Troubleshooting

Issue	Possible Causes	Solutions
Command not executed	Security authorization insufficient Syntax error in command	Check security profiles for command authority Verify command syntax is correct
Command response not visible	Responses go to system log, not job log Command issued to wrong subsystem	Check SYSLOG or console logs for responses Specify correct REL= parameter
JCL error on COMMAND statement	Missing quotes around command Invalid command syntax	Ensure command is enclosed in single quotes Check JCL syntax for COMMAND statement
Command rejected by system	Command not valid in current system state Resource not available	Check system status before issuing command Add prerequisite steps to ensure proper state

Debugging Tips

Test commands interactively at console before using in JCL
Monitor SYSLOG during job execution to see command responses
Use the TYPRUN=SCAN JOB parameter to validate JCL without executing commands
Add extra display commands to show system state before and after critical commands
Implement command verification steps that check if commands had the desired effect

JES2 vs JES3 Considerations

Feature	JES2	JES3
Command Prefix	Typically $ (e.g., $D I)	Typically * (e.g., *I,J=jobname)
Command Structure	Usually more concise	Often more verbose with commas
Command Validation	JES2 command validation	JES3 command validation
Alternative Method	/*$command syntax	//*command syntax

Alternatives to COMMAND

JES2 Command Format: /*$command - alternative for JES2 commands
JES3 Command Format: //*command - alternative for JES3 commands
CNTL/ENDCNTL Statements: For more complex command sequences
Started Tasks: For extensive operator command sequences
Automation Tools: Products like CA OPS/MVS, IBM System Automation

Related Concepts

CNTL/ENDCNTL Statements - Provides a way to include multiple commands in a control group
JCL Security - Security considerations for command issuance
Conditional Execution - Can be used with commands for more complex automation
JES2 Commands - Reference for commands that can be issued via COMMAND
JES3 Commands - Reference for JES3-specific commands
MVS System Commands - Reference for system commands that can be used