Quoted from Wikipedia:By default, when a process is created it inherits a duplicate  environment of its parent process, except for explicit changes made by  the parent when it creates the child. At API level, these changes must  be done between fork and exec. Alternatively, from shells such as  bash, you can change environment variables for a particular command  invocation by indirectly invoking it via env or using the  ENVIRONMENT_VARIABLE=VALUE  notation.I understand that when a process is created it inherits a duplicate environment of its parent process. But I was wondering what the exception explicit changes made by the parent when it creates the child really means? I don't understand how the examples in API and shells are examples of the exception.
Exception of inheritance of environment variables
environment variables