Environment Variable APIs

Environment variables are character strings of the form "name=value". There are two types of environment variables:

• Job-level environment variables. The job-level environment variables are stored in an environment space outside of the program associated with the job. They can be manipulated by using the getenv(), putenv(), Qp0zDltEnv(), Qp0zGetEnv(), Qp0zInitEnv(), and Qp0zPutEnv() APIs, as well as the CL commands ADDENVVAR, CHGENVVAR, RMVENVVAR, and WRKENVVAR. These variables exist for the duration of the job or until they are deleted. There is a limit of 4095 job-level environment variables.

• System-level environment variables. The system-level environment variables are stored in a global environment space that is persistent across IPLs and is not associated to a particular job. They can be manipulated by using the Qp0zDltSysEnv(), Qp0zGetAllSysEnv(), Qp0zGetSysEnv(), and Qp0zPutSysEnv() APIs, as well as the CL commands ADDENVVAR, CHGENVVAR, RMVENVVAR, and WRKENVVAR. These variables exist until they are deleted. There is a limit of 4095 system-level environment variables.

When a job calls one of the job-level environment variable APIs or CL commands for the first time, it inherits the system-level environment variables onto its job-level environment space. Any changes to job-level and system-level environment variables are then independent of one another.

The temporary space where the job-level environment variables are stored allows read and write access. Therefore, it is possible for the space to be corrupted. This could occur if a programmer accesses the space directly using the environ array rather than using the environment variable APIs. If the space is corrupted, subsequent calls using the APIs will have unpredictable results.

Environment Variable APIs--Summary

Figure 1-1 lists the environment variable functions and what they do.

Figure 1-1. Environment Variable Functions

Function	Description
getenv()	Get value of environment variable
putenv()	Change or add environment variable
Qp0zDltEnv()	Delete an environment variable
Qp0zDltSysEnv()	Delete a system-level environment variable
Qp0zGetAllSysEnv()	Get all system-level environment variables
Qp0zGetEnv()	Get value of environment variable (extended)
Qp0zGetSysEnv()	Get value of system-level environment variable
Qp0zInitEnv()	Initialize environment for variables
Qp0zPutEnv()	Change or add environment variable (extended)
Qp0zPutSysEnv()	Change or add a system-level environment variable

Note: These functions use header (include) files from the library QSYSINC, which is optionally installable. Make sure QSYSINC is installed on your system before using any of the functions. See Header Files for UNIX-Type Functions for the file and memeber name of each header file.