I. Purpose

The purpose of the assignment was to challenge the students to create a shell program. The shell program will run commands in one of two
ways. If the user just runs the executable, the shell will run in interactive mode. If an input file is provided, the shell will run in batch mode. In interactive mode, the user is prompted to manually enter commands. The program will execute the commands and the user
will be prompted again. The program will continue to run until the user enters “quit.” In batch mode, the program will execute the commands in the input file one line at a time. After the commands have run, the program ends.

II. File List

• shell.c
• batch1
• batch2
• README.md
• Makefile

III. Compiling the assignment

Simply upload all the file to your directory and run "make" to compile all the included files,in this case, we only have one .c file. (no separate header files or .c are included)

VI. Instructions

1. Unzip files
2. Enter "make" into command prompt
3. Type "./shell" into command prompt
4. Enter in Commands
5. Seperate commands with "; "

V. Design Overview

The program is set up using a struct array to hold the commands. Each struct has a command name, a command type, the command(s), and the argument count. During program startup, the program checks for the initial number of arguments. If the argument count is 1, then the program will run in interactive mode. If the argument count is 2, then the program will run in batch mode. The program will then get setup to run in either mode, but the shell execution runs the same either way once the commands are pulled.

The program then inputs the commands into the struct array. The
commands are then parsed. Each command gets any extra characters and spaces trimmed. During parsing, the program also checks for special commands, such as exit, history, or prompt. To execute the commands, the command is run through a child process via execvp. If the command is a special command, then the command is sent to a function to be executed manually. After the commands run, the shell resets the array and prepares to run the next command. In interactive mode, the user is prompted again, and in bash mode, the shell pulls the next commands. This repeats until all the commands are ran or the interactive mode ends.

For ambiguities, the code has a few methods for dealing with them. For extra semicolons, the program reads commands until it finds a semicolon, so having a few semicolons next to each other will just be read over. Extra white spaces will be trimmed off in the trim function. No commands will just be passed over so those are not an issue.