Why do CD commands need built-in shell commands?

If you do not use the built-in command but fork to output a sub-process and execute it in the sub-process, the path of the parent environment will not be changed.

After the execution is completed, it returns to the parent shell environment, and the PWD of the environment is not changed at all, so it will fail.

You can write a script to test CD. Sh.

#! /Bin/bash
CD/home/

Run./CD. SH and you will find that the current shell path has not changed.

Similarly, if you want to change many parameters of the current shell and the content of the Environment Variable table, you must use built-in commands.