Setting z/OS XL C/C++ environment variables from JCL

If you are starting the z/OS® XL C⁄C++ UNIX application from JCL, you must code the environment variable as a parameter in the JCL of the application, as shown in the following examples:

This example shows setting the RESOLVER_CONFIG environment variable to a z/OS UNIX file:

//OSNMPD    PROC
//*
//* Procedure for running the SNMP agent
//*
//OSNMPD EXEC PGM=EZASNMPD,REGION=4096K,TIME=NOLIMIT,
// PARM=('POSIX(ON) ALL31(ON)',
//      'ENVAR("RESOLVER_CONFIG=/etc/tcpa.data")/-d 0')
⋮

This example shows setting the RESOLVER_CONFIG environment variable to an MVS™ partitioned data set:

//OSNMPD    PROC
//*
//* Procedure for running the SNMP agent
//*
//OSNMPD EXEC PGM=EZASNMPD,REGION=4096K,TIME=NOLIMIT,
// PARM=('POSIX(ON) ALL31(ON)',
//  'ENVAR("RESOLVER_CONFIG=//''TCPA.MYFILE(TCPDATA)''")/-d 0')
⋮

This example shows setting the RESOLVER_CONFIG environment variable to a DD card:

//OSNMPD PROC
//*
//* Procedure for running the SNMP agent
//*
//OSNMPD EXEC PGM=EZASNMPD,REGION=4096K,TIME=NOLIMIT,
// PARM=('POSIX(ON) ALL31(ON)',
// 'ENVAR("RESOLVER_CONFIG=DD:TCPDATA")/-d 0')
//TCPDATA DD DSN=TCPA.MYFILE(TCPDATA),DISP=SHR
⋮

Tip: You can also specify a ddname as //DD:ddname, as shown in the following example:

⋮
// 'ENVAR("RESOLVER_CONFIG=//DD:TCPDATA")/-d 0')

For more information about specifying a ddname, see z/OS XL C/C++ Programming Guide.

This example shows how you can set environment variables using the STDENV DD statement. The environment variables will be read from the location specified by the STDENV DD statement. The advantage of using STDENV is that it eliminates any concern about the maximum number of characters that can be specified on the PARM= parameter of the EXEC JCL statement. Perform the following steps to set environment variables using the STDENV DD statement:
1. Create the MVS data set that will contain the environment variables with a variable length record format (RECFM=V/VB).
  This example uses an MVS data set TCPA.ENVAR(OSNMPD).
  
  Rule: Do not use fixed length record format (RECFM=F/FB) to allocate the MVS data set because fixed length pads the environment variables with blanks.
2. Edit the MVS data set so that it contains the environment variables.
  The following example shows setting the RESOLVER_CONFIG environment variable to a file:
```
RESOLVER_CONFIG=/etc/tcpa.data
```
  The following example shows setting the RESOLVER_CONFIG environment variable to an MVS data set:
```
RESOLVER_CONFIG=//’TCPA.MYFILE(TCPDATA)’
```
3. Update the application's JCL to pick up the TCPIP.DATA information from the specified RESOLVER_CONFIG environment variable.
```
//OSNMPD PROC
//*
//* Procedure for running the SNMP agent
//*
//OSNMPD EXEC PGM=EZASNMPD,REGION=4096K,TIME=NOLIMIT,
// PARM=(’POSIX(ON) ALL31(ON)’,
// ’ENVAR("_CEE_ENVFILE=DD:STDENV")/-d 0’)
//STDENV DD DSN=TCPA.ENVAR(OSNMPD),DISP=SHR
```
For more information about specifying a list of environment variables using the _CEE_ENVFILE environment variable, see z/OS XL C/C++ Programming Guide.