Minishell

A mini Unix shell implemented in C demonstrating process control, signal handling, and interaction with the Linux /proc filesystem. Developed for CS 392 Systems Programming.

Overview

Minishell is a custom command-line interpreter built from scratch in C. The project showcases low-level systems programming techniques including subprocess creation, directory and filesystem traversal, manual parsing, resource management, and signal-safe I/O.

The repository includes a compiled executable (minishell) as well as the full source implementation.

Core Capabilities

Built-in Commands

Command	Description
cd, cd <path>	Changes the working directory; supports home directory (~), absolute, and relative paths.
pwd	Prints the full current working directory.
lf	Lists non-hidden files in the current directory.
lp	Enumerates active system processes by scanning the /proc filesystem.
exit	Frees allocated resources and exits the shell.

External Program Execution

If a command is not a built-in, the shell delegates execution to the OS using:

• fork() to spawn a child process
• execvp() to replace the child process image
• wait() to synchronize with the parent

Supports variable-length argument lists up to 50 tokens.

Process Listing (lp)

lp replicates a simplified version of top by reading from /proc/[pid]/:

• Extracts PID from directory names
• Reads the program’s command line from cmdline
• Retrieves the associated user from system password entries
• Stores results in an array of process structs
• Sorts the list numerically by PID

This demonstrates direct interaction with the Linux /proc virtual filesystem and parsing of kernel-generated process information.

Signal Handling

Minishell implements a custom handler for SIGINT (Ctrl+C):

• Foreground child processes receive the interrupt
• The shell itself remains active
• Interruptions during getline() are detected through a volatile sig_atomic_t flag

Running the Shell

Optional: Recompile from source

gcc minishell.c -o minishell 

Using the executable:

./minishell