DragonShell

An easy to use Linux Shell

Design Choices

• Command Handling: Commands are basically just done by tokenizing an arg string. The built-in commands (pwd, cd, exit) are handled in the arg_handler function, while external commands are managed in external_cmds.

• Input/Output Redirection: Copy the read and write files into their own strings. If set then open the respective files for redirection.

• Piping: Spilt the commands into 2 argv variables On process is forked and parent handles the other. Parent get results from child.

• Signal Handling: Basically just created handlers that send the signals to the processes that are running and not the shell. sigchld is for preventing zombies.

• Background: Just a flag. If set we will just not tell the shell to wait for the process to finish.

System Calls Used

The following system calls were used:

• fork(): Used for running external programs in new processes.
• execve(): Used to execute external programs.
• waitpid() & wait(): Used to wait for child processes to finish.
• kill(): exiting the shell, sending signals for signal handler.
• pipe(): piping.
• chdir(): Used to change the current working directory.
• getcwd(): Used to get the current working directory.
• open(): Used to open files for input/output redirection.
• dup2(): Used to duplicate file descriptors for redirection.

Testing

The shell was tested through various command scenarios to ensure all features were functioning as intended. The testing process included:

1. Basic Command Execution: Tested built-in commands (pwd, cd, exit) to verify their functionality. Afterwards external commands were tested (ls, cat, find, as well as my own custom programs)
2. Input/Output Redirection: Followed the testing with a.out reference in the assignment doc. Did output redir to create a.out and then tested input redir with cat
3. Piping: Followed the find sort example in the assignment doc
4. Signal Handling: Tested with wait.c which provided from lab 1
5. Background Processes: Launched processes with & to verify they could run independently without blocking the shell.

Sources

• Die.net