The document discusses UNIX shells and their functions as an interface between users and the operating system hardware, including how shells allow for command execution, scripting, and redirection of standard input/output/error. It also covers common shell features like tab completion, history, aliases, environment variables, job control, and process management using commands like ps, kill, and pgrep.

1. Lecture 4<br />ShellUserUNIX shells:<br />HWWhy it is called shell??<br />Layer between the hardware and the user

2. Command Line interface

3. Function:

4. Interpreter ls * ls f1 f2 f3 common in all shells

5. Shell scripts (programs) differ in syntax from one shell and another

6. Features <br />History

7. Auto CompletionBash tab<br />Kshesc \ you must be in vi mode <br />esc = all occurance<br />Redirection

8. Default action of the commandCommand takes the standard input from the keyboard and sends the standard output to the terminal window.<br />You can modify the default action of the standard input, standard output, and standard error within the shell by redirecting stdin, stdout, and stderr.<br />19558090170

9. Input redirection: