Simple Shell

A minimalist UNIX command line interpreter implemented in C.

Overview

This shell project is a streamlined implementation of a command-line interpreter that provides essential shell functionality. It handles both interactive and non-interactive modes, command execution, PATH resolution, and basic built-in commands.

Features

• Interactive command prompt ($)
• Command execution with arguments
• PATH environment variable handling
• Built-in commands: exit and env
• Error handling with appropriate exit statuses
• Memory management
• Non-interactive mode support (commands from pipes)

Flowchart

graph TD
    A[Start] --> B{Interactive Mode?}
    B -->|Yes| C[Display Prompt]
    B -->|No| D[Read Command]
    C --> E[Read Command]
    E --> F[Parse Command]
    D --> F
    F --> G{Built-in Command?}
    G -->|Yes| H[Execute Built-in]
    G -->|No| I{Contains Path?}
    I -->|Yes| J[Check if Executable]
    I -->|No| K[Search in PATH]
    J --> L{Executable?}
    K --> L
    L -->|Yes| M[Fork Process]
    L -->|No| N[Print Error]
    M --> O[Execute Command]
    O --> P[Wait for Child]
    H --> Q{Exit Command?}
    P --> Q
    N --> Q
    Q -->|Yes| R[Exit Shell]
    Q -->|No| B

Loading

Technical Details

Command Processing Flow

1. Input Reading:

   • Interactive mode: Display prompt and read user input
   • Non-interactive mode: Read from pipe/file

2. Command Parsing:

   • Remove leading/trailing spaces
   • Split command into arguments
   • Handle special characters

3. Command Execution:

   • Check for built-in commands
   • Search in PATH if no explicit path
   • Fork and execute command
   • Handle errors and return status

Built-in Commands

1. exit [status]:

   • Exit the shell with optional status
   • Default status: 0
   • Handle illegal status numbers

2. env:

   • Print current environment variables
   • No arguments supported

Error Handling

• Command not found: Exit status 127
• Permission denied: Appropriate error message
• Memory allocation failures: Proper cleanup
• Fork failures: Error message and continue

Compilation

gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o hsh

Usage

Interactive Mode

$ ./hsh
$ ls
hsh main.c shell.h
$ pwd
/home/user/simple_shell
$ exit
$

Non-interactive Mode

$ echo "ls" | ./hsh
hsh main.c shell.h
$ cat test_script | ./hsh
[script output]

Environment

• Tested on Ubuntu 20.04 LTS
• Compiled with gcc 9.4.0
• Follows Betty style guidelines

Files Description

• main.c: Main shell loop and input handling
• execute.c: Command execution functions
• path.c: PATH handling and command location
• builtins.c: Built-in command implementations
• shell.h: Header file with prototypes and structures

Author

Edwin : https://github.com/neodwin
Ewan : https://github.com/DARcodertech
Frederic : https://github.com/FredBourouliou