BigShell: POSIX Shell Clone

BigShell is a custom-built command-line shell that emulates core behaviors of a POSIX-compliant shell. It was developed as a senior project to explore advanced system-level programming concepts in C, including process management, I/O redirection, signal handling, and environment variable manipulation.

Note: Due to academic integrity restrictions, source code is not published in this repository. Only compiled binaries, screenshots of test runs, and the final technical report are provided.

---

Project Showcase

• Screenshots: BigShell supports key POSIX shell features including built-ins, job control, pipelines, I/O redirection, and signal handling.

The following categories are demonstrated in annotated test examples:

• exit built-in with custom status codes
• Variable assignment and export to environment
• Output redirection (>), with overwrite protection
• Command pipelines using | (e.g., echo | sed | cat)
• Signal handling (e.g., SIGINT, SIGTSTP, SIGTTOU)
• Background jobs with $! tracking

View annotated terminal tests and screenshots:
BigShell_Annotated_Tests.pdf

• Executable Binaries:
  • release/ — optimized build
  • debug/ — debug symbols included
• Documentation:
  • Full system report: BigShell_Report.pdf

---

Features Implemented

BigShell handles a significant subset of POSIX shell functionality, including:

• Built-in Commands:
  cd, exit, unset, export, pwd, fg, bg, jobs

• External Command Execution:
  Run binaries available in $PATH

• Pipelines:
  Chain commands using | operator

• I/O Redirection:
  Support for <, >, >>, <>, >|, <&, >&

• Environment Variables:
  Assignment, export, evaluation ($VAR, ${VAR}, ~ expansion)

• Foreground/Background Jobs:
  Commands run with ; (foreground) or & (background)

• Signal Handling:
  Intercept SIGINT, SIGTSTP, and forward signals to child processes

---

Learning Takeaways

This project was a deep dive into:

• POSIX system calls (fork, execvp, waitpid, pipe, dup2, kill, tcsetpgrp)
• Shell parsing techniques and token expansion
• Job control and process group management
• File descriptor manipulation and redirection
• Debugging with gdb in a remote server environment

---

Build Instructions

The project includes a Makefile to streamline compilation:

make           # Builds both release and debug versions
make release   # Builds optimized executable in release/
make debug     # Builds debug executable with symbols in debug/
make clean     # Removes all build artifacts (release/ and debug/)

Output Structure

• release/bigshell – Optimized executable (no debug output)
• debug/bigshell – Debug build with assertions and verbose messages

To run the shell:

cd release/
./bigshell

To debug:

cd debug/
gdb ./bigshell

---

Documentation

See the final report: BigShell_Report.pdf

Screenshots: available under docs/screenshots/

---

Directory Structure

.
- release/                                  # Compiled release version
- debug/                                    # Compiled debug version with symbols
- docs/
  -- CS374_BigShell_Report_113024_v04.docx  # Full project report
  -- screenshots/                           # Images of the shell in action
- README.md                                 # This file

---

Author

Built with C and grit.
See more projects at https://github.com/Luckygoldjade