exec

The exec is a command line tool in Unix-like operating systems that is used to execute a new process, replacing the current process. When exec is called, it loads a new program into the current process, thereby replacing the existing code, data, and stack with the new program's.

Some important points about the exec command:

1. exec is often used in shell scripts to replace the current shell with a different program. This is commonly seen when a shell script invokes another script or binary executable.

2. The exec command does not create a new process; it essentially loads a new program into the current process. This means that any further commands or statements after exec in a shell script will not be executed.

3. There are different variants of exec including execvp, execve, etc., each with its specific functionality. For example, execvp searches for the executable file in directories listed in the PATH environment variable.

4. exec also allows passing command line arguments to the new program being executed.

5. When exec is used, the new program replaces the existing process, including its process ID (PID), environment variables, and file descriptors. This means any open files or network connections from the previous process will be inherited by the new program.

6. It's important to note that exec does not return control to the calling process unless there is an error, in which case it will return a non-zero exit code.

7. The exec command can be used in combination with other shell commands and operators, like fork, to create more complex execution flows.

Overall, exec is a powerful command line tool that allows for the seamless execution of different programs within a single process, letting the new program take over the current process completely.