Example: Running a shell command in batch

In the following example, BPXBATCH runs the shell command compress to compress the file /usr/lib/junk. To start the next JCL job step before the compress command completes, the parameter string is specified as:

SH nohup compress /usr/lib/junk & sleep 1

If, instead, the parameter string is specified as:

SH compress /usr/lib/junk

the job step waits for the compress shell command to end. For short-running commands, this is fine.

For long-running commands, however, where you want to use BPXBATCH to start a shell command in the background and not wait for completion, you must specify the parameter string like this:

SH nohup command args & sleep 1

SH starts a login shell to parse and run the command. The login shell parses the &, signifying that the command is to run asynchronously (in the background), and forks a child process to run the nohup command. In the child process, the nohup shell command (which takes another command as an argument) prevents the process from being terminated when the login shell returns to BPXBATCH.

In parallel with the nohup processing, the login shell runs the sleep command. Running the sleep command delays the login shell from returning to BPXBATCH until the child process has had enough time (1 second) to protect itself from being terminated. The login shell returns to BPXBATCH, while the child process continues to run the compress command.

Example: User TURBO runs the compress shell command in batch, as follows:

STDPARM defines an in-stream data set containing the parameter string.
STDERR defines a file to which to write error messages, /u/turbo/bin/mystd.err.
The STDIN and STDOUT files default to /dev/null.
The STEPLIB is propagated for the execution of the shell and for any processes created by the shell.

//jobname  JOB  ...
//stepname EXEC PGM=BPXBATCH,REGION=8M
//STEPLIB  DD   DSN=CEE.SCEERUN,DISP=SHR
//STDERR   DD   PATH='/u/turbo/bin/mystd.err',
//              PATHOPTS=(OWRONLY,OCREAT,OTRUNC),PATHMODE=SIRWXU
//STDPARM  DD   *
SH nohup compress /usr/lib/junk & sleep 1
/*

Example: The following JCL is similar to the previous example and produces equivalent results but uses PARM= to specify the parameter string:

//jobname  JOB  ...
//stepname EXEC PGM=BPXBATCH,REGION=8M,
//              PARM='SH nohup compress /usr/lib/junk & sleep 1'
//STEPLIB  DD   DSN=CEE.SCEERUN,DISP=SHR
//STDERR   DD   PATH='/u/turbo/bin/mystd.err',
//              PATHOPTS=(OWRONLY,OCREAT,OTRUNC),PATHMODE=SIRWXU