Shell Description

This comprehensive overview provides details on external and internal commands implemented in the shell, along with error-handling mechanisms. Additionally, test cases and assumptions are outlined to guide users in utilizing the shell effectively.

External Commands

1. ls

- ls -a
- ls -m

2. cat

- cat -n
- cat -E

3. date

- date -u
- date -I

4. rm

- rm -v
- rm -i

5. mkdir

- mkdir -p
- mkdir -v

Internal Commands

1. cd

- cd ~
- cd ..

2. echo

- echo *
- echo --help

3. pwd

- pwd -L
- pwd -P

Error Handling

1. Command Not Found: If the user enters any command other than the specified ones.
2. No Such File or Directory: In cat and rm commands for non-existing files, and in cd for non-existing directories.
3. Invalid Option: If the user enters an option not handled by the shell.
4. Missing Operands: In cat if the user enters it without any argument.
5. Cannot Create Directory: In mkdir if the user tries to create a duplicate directory.
6. Fork Error (Child Process Not Created): Error handling for creating a child process using the Fork System Call.

Implementation Details

The shell can be implemented using both forks and threads. If someone wishes to use threads, they can add &t at the end of the command. For example:

• ls -a &t
• cat -n cat.c &t
• date -I &t

Test Cases

1. ls

• ls -a & ls -a &t
• ls -m & ls -m &t

2. cat

• cat -n cat.c & cat -n cat.c &t
• cat -E cat.c & cat -E cat.c &t

3. date

• date -u & date -u &t
• date -I & date -I &t

4. rm hello.c

• rm -v hello.c & rm -v hello.c &t
• rm -i hello.c & rm -i hello.c &t

5. mkdir newDir

• mkdir -p newDir/newDir2 & mkdir -p newDir/newDir2 &t
• mkdir -v newDir & mkdir -v newDir &t

Assumptions

1. No unnecessary arguments will be passed in between or after the command.
2. cat and rm commands will not be passed a directory as an argument.
3. mkdir and rm commands will not be entered without any arguments.