Final answer:
In Unix, a child process is created with the fork() system call, which duplicates the current process. The child process can execute different code using the exec() family of calls, while the parent may wait for the child's completion using wait().
Step-by-step explanation:
In the Unix operating system programming environment, a new (child) process is created using the fork() system call. The fork() function creates a new process by duplicating the current process. The new process, referred to as the child, is an exact copy of the calling process, known as the parent, except for some unique values such as process ID. After a successful fork() call, both the parent and the child processes will execute the subsequent code, and they can identify their roles by checking the return value of fork(). A return value of zero indicates that the current process is the child, while a non-zero value, specifically the child's process ID, is returned to the parent process. If there is an error in creating a child process, fork() will return -1.
Additionally, the exec() system call family can be used by the child process to replace its process image with a new program. This allows the child process to execute different code from the parent process. Another related system call is wait(), which the parent process can use to wait for the child process to complete its execution before continuing.