shell-ish

Ata Berke Göktekin 80277

A Unix-style interactive shell implemented in C for COMP 304 Assignment 1.

Repository

GitHub: https://github.com/AtaGoktekin/shell-ish

How to Build & Run

gcc -o shell-ish shellish-skeleton.c
./shell-ish

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Features

Part I — Command Execution & Background Processes

Shell-ish executes standard Linux commands by manually resolving the PATH environment variable using execv() (not execvp()).

ls -la
mkdir test
date
gcc -o hello hello.c

Background execution with & — shell returns to prompt immediately:

sleep 10 &
# [background] PID: 12345

Part II — I/O Redirection & Pipes

Output redirection (truncate):

ls -la >output.txt

Output redirection (append):

ls >>output.txt

Input redirection:

cat <output.txt

Note: No space between redirection symbol and filename (e.g. >file.txt not > file.txt)

Piping — single and chained:

ls -la | grep shell
ls -la | grep shell | wc
cat /etc/passwd | cut -d : -f 1,6

Part III — Builtin Commands

cut — Field Extractor

Reads lines from stdin and prints specified fields. Implemented in C.

Options:

• -d <char> or --delimiter <char> — field delimiter (default: TAB)
• -f <list> or --fields <list> — comma-separated list of field indices (1-based)

cat /etc/passwd | cut -d : -f 1,6
# root:/root
# bin:/bin
# ...

echo -e "a\tb\tc" | cut -f 2
# b

chatroom — Group Chat via Named Pipes

Simple multi-user chat using named pipes under /tmp/chatroom-<roomname>/.

chatroom <roomname> <username>

• Creates the room folder if it doesn't exist
• Creates a named pipe for the user
• Receives messages from others continuously (reader child process)
• Sends messages to all other users in the room
• Type exit to leave the room

Example (open two terminals):

# Terminal 1:
chatroom comp304 ali

# Terminal 2:
chatroom comp304 mehmet

remind — Terminal Reminder

Sets a reminder that appears after a specified number of seconds.

remind <seconds> <message>

Examples:

remind 10 tea time!

After the specified time:

--------------------
REMINDER: tea time!           
--------------------

How it works: remind forks a child process that calls sleep() for the given duration, then prints the message. The parent returns immediately so the shell stays responsive.

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File Structure

shellish/
├── shellish-skeleton.c   # full shell implementation
├── README.md             # this file
├── imgs/                 # screenshots of each feature
│   ├── part1_exec.png
│   ├── part1_background.png
│   ├── part2_redirection.png
│   ├── part2_pipe.png
│   ├── part3_cut.png
│   ├── part3_chatroom.png
│   └── part3_remind.png

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Notes

• Tested on macOS
• cut is implemented as a shell builtin (not an external binary)
• chatroom uses mkfifo for named pipes under /tmp/
• remind uses fork + sleep to avoid blocking the shell

Assistance

During the development of this readme and bugs on the project, ChatGPT was used for assistance in the following areas:

• Debugging compiler errors and warnings (e.g. implicit function declarations, buffer truncation warnings)
• Fixing the termios canonical mode issue in the chatroom command
• Writing and formatting this README