Introduction - If you have any usage issues, please Google them yourself
Write their own shell, its function as follows:
1) cd <directory>- The current default directory is changed to <directory>. If there is no <directory> parameter, it displays the current directory. If the directory does not exist, there will be an appropriate error message. This command can also change the PWD environment variable.
2) clr- clear the screen.
3) <directory>- list directory <directory> content.
4) environ- lists all environment variables.
5) echo <comment>- Display <comment> on the screen and a line feed (multiple spaces and tabs may be reduced to a single space).
6) help- displays the user s manual, and use the more command filtering.
7) quit- quit she