Simple-shell

This is programming project 1 in chapter 3 of the book Operating system concepts 10th ed. (Silberschatz, Galvin, and Gagne)

This program acts as a simple shell:

1. It can receive and execute Unix commands (with arguments)
2. Pipe and IO redirection features: It provides pipe (!) or IO redirection (for one file only) (< or >) features
3. However, only one of these features can be used per command, and at one time only per command (i.e. there may not be two pipes, or a pipe and an IO redirection in the same command).
4. History feature: To execute the most recent command, simply enter !!
5. Background feature: To execute the command in the background and move on with the shell, * add & after a command
6. To exit the program, simply run the command exit

*Note: Not all commands will run. The implementation of the shell is very basic, using execvp() to run commands.

How to run (for beginner programmers):

1. Compile and run the program: gcc -o shell simple-shell.c && ./shell
2. Or just run compiled program: ./shell

Test commands:

1. pwd (output full path name of the current directory)
2. cat defs.h > sample.txt & (read the file defs.h and redirect the output to sample.txt in the background)
3. wc -l < defs.h (list the number of lines in defs.h)
4. ls | sort (output the (sorted) items in a directory)
5. !! & (run previous command in the background)