Minishell

Minishell is a Unix-style command-line shell implemented in C.
The project focuses on process management, command parsing, directory navigation, and interaction with the /proc virtual filesystem.

The shell is implemented from scratch without external shell libraries, using low-level system calls for process creation, execution, and signal handling.

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Overview

Minishell accepts user input, tokenizes commands, executes supported built-ins internally, and runs external programs using fork() and execvp().

The shell maintains a prompt that reflects the current working directory and handles keyboard interrupts without terminating the session.

The repository includes:

• the full source implementation (minishell.c)
• a precompiled executable (minishell, macOS build)

Recompiling locally is recommended for portability.

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Core Capabilities

Built-In Commands

Command	Description
cd <path>	Changes the working directory. Supports ~, absolute, and relative paths.
pwd	Prints the current working directory.
lf	Lists visible files in the current directory (excluding . and ..).
lp	Enumerates running system processes via /proc.
exit	Cleanly terminates the shell.

If a command is not one of the built-ins, Minishell treats it as an external executable.

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External Program Execution

Minishell runs external programs using the standard Unix process model:

• fork() — creates a child process
• execvp() — replaces the child with the requested program
• wait() — synchronizes execution with the parent

Commands such as:

ls
cat file.txt
echo hello

execute in the foreground through a spawned process.

Arguments are tokenized prior to execution.

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Process Listing (lp)

The lp command provides a basic process viewer by scanning /proc.

For each numeric PID entry, Minishell:

• extracts the PID from the directory name
• reads the command line from /proc/<pid>/cmdline
• retrieves the associated username from system password records
• stores process entries in an array
• sorts them numerically
• prints results in aligned columns

This demonstrates interaction with:

• the /proc virtual filesystem
• kernel-generated process metadata
• filesystem traversal and user lookup

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Signal Handling

Minishell registers a custom SIGINT handler for Ctrl-C.

Behavior:

• foreground child processes receive the interrupt
• the shell remains active
• interrupted input lines reset cleanly
• state is tracked using a volatile sig_atomic_t flag

This allows interruptions without terminating the shell session.

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Building

Compile from source

gcc minishell.c -o minishell

Run the shell

./minishell