This article examines the fundamental concepts of fork() and exec() in Unix programming.

The fork() system call is utilized to create a new process by duplicating an existing one. Both the parent process and the child process generated by fork() are identical, with the exception of the return value. In the parent process, the return value represents the process identifier (pid) of the child process, while in the child process, the return value is 0.

On the other hand, the exec() system call is employed to replace the current process with a new program. Although it is independent of fork(), exec() is often used in conjunction with fork() when launching a different child process. Exec() loads a new program into memory and executes it, essentially replacing the existing program.

In summary, fork() is employed to create a copy of the running process, whereas exec() is used to replace the current process with a new one. These two concepts are commonly utilized in tandem to launch new programs.

Concepts of fork()

The concept of fork() in Unix programming involves the creation of a new process by duplicating the existing process.

When the fork() system call is invoked, a copy of the running process is created.

The parent process and child process are identical except for the return value of fork().

The parent process receives the process identifier (pid) of the child process as the return value of fork().

The child process, on the other hand, receives 0 as its return value.

The fork() system call is commonly used in conjunction with the exec() system call to launch new programs.

For example, the shell uses fork() to launch commands.

It forks a child process, and the child process then executes the associated command.

Concepts of exec()

Exec() is a system call that replaces the current process with a new program, effectively loading a new program into the memory and executing it.

It is important to note that exec() has nothing to do with fork(), but it is often used after fork() to launch a different child process.

When exec() is called, the current process is completely replaced by the new program, and the new program starts executing from its main() function.

The new program can have different code, data, and stack segments than the previous program, allowing for a completely different execution environment.

The exec() system call is commonly used by the shell to execute commands entered by the user.

By using exec(), the shell can load and execute different programs based on the user’s input, effectively providing a versatile and interactive experience.

Common concepts

A fundamental concept in Unix programming is the ability to create new processes and replace them with different programs. This is achieved through the use of fork() and exec() system calls.

The shell, which is the command interpreter in Unix, supports three types of commands: executable files, executable files containing shell command lines, and internal shell commands.

When a command is entered by the user, the shell interprets the first word as the command name. It then forks a child process and the child process executes the command with the given parameters using exec().

The fork() system call creates a copy of the running process, while exec() replaces the current process with a new program. The fork() call returns the process identifier (pid) of the child process in the parent, and 0 in the child process.

On the other hand, exec() loads a new program into memory and executes it.