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PS4 - Simple Shell with Pipes

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@Brawun Brawun released this 23 Nov 05:29
release1.ps4
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My Simple Shell

SimpleShell is a simple, interactive shell program written in C++. It allows users to enter basic commands, which are then executed as separate processes. The shell provides basic functionality, such as command parsing and execution, through a continuous loop that reads user input, interprets the command, and displays results. This shell program is intentionally minimal, making it a starting point for learning shell basics and process management in C++.

Features

  • Command Parsing: User inputs are tokenized into commands and arguments, allowing a variety of commands with arguments.
  • Command Execution: Each command runs in a child process, created using fork() and executed with execvp().
  • Looping Prompt: The shell continuously prompts users for commands until they signal EOF (e.g., Ctrl+D).
  • Input/Output Redirection: Supports redirection of input and output using < and > symbols. For example, command < input.txt > output.txt redirects standard input from input.txt and standard output to output.txt.
  • Pipe Handling: Supports command piping using | to pass the output of one command as input to another. For example, cat file.txt | grep pattern.
  • Basic Error Handling: Provides feedback for failed executions or invalid commands.

Program Structure

  • SimpleShell.h: Defines the SimpleShell class, including methods for running the shell loop, parsing input, and executing commands.
  • SimpleShell.cpp: Implements the SimpleShell class, containing the core functionality of the shell.
  • Makefile: A Makefile for compiling, running, and cleaning up the program.

File Descriptions

  • SimpleShell.h: Header file containing the declarations of the shell methods and class structure.
  • SimpleShell.cpp: Source file with the full implementation of the shell’s features, including command parsing, execution, and pipe handling.
  • Makefile: Used to compile, run, and clean the program with simple commands.

How to Build and Run the Program

Prerequisites

  • C++ Compiler: Ensure you have a C++11-compatible compiler installed (e.g., g++).
  • Make: Make should be installed to use the Makefile commands.

Compilation and Execution

Open a terminal in the project directory and use the following commands:

make           # Compiles and runs the program
make compile   # Only compiles the program and creates an executable in bin/
make run       # Executes the compiled program
make clean     # Cleans up object files and the executable in bin/

Using SimpleShell

  1. Run the shell using make or make run.
  2. When the prompt SimpleShell % appears, type any standard command (e.g., ls, pwd, echo Hello).
  3. Press Enter to execute the command.
  4. To exit the shell, type Ctrl+D or terminate the process.

Example Session

SimpleShell % ls
file1.cpp  file2.cpp  SimpleShell.cpp  bin

SimpleShell % echo "Hello, SimpleShell!"
Hello, SimpleShell!

SimpleShell % pwd
/home/user/Simpleshell

SimpleShell % cat < input.txt | grep pattern > output.txt

SimpleShell % invalidcommand
Execution failed: No such file or directory

SimpleShell % Ctrl+D

Code Overview

  • Shell Loop (run()): The main loop displays the prompt, reads user input, parses it, and executes the command.
  • Command Parsing (parse()): Splits the input string by spaces to form a command and argument list.
  • Command Execution (execute()): Uses fork() to create a new process and execvp() to run the command in the child process. Handles input and output redirection using < and > and handles pipes (|) for command chaining.

Future Extensions

SimpleShell is designed as a minimalistic shell, ideal for adding more advanced features, such as:

  • Append Output Redirection: Supporting >> to append output to a file.
  • Signal Handling: Implementing custom handling for signals (e.g., Ctrl+C to terminate commands).
  • Environment Variables: Supporting access and modification of environment variables.
  • Command History: Adding support for maintaining a history of commands, allowing users to recall previous commands easily.

Troubleshooting

  • "Execution failed" Error: If a command cannot be found, ensure it’s installed and accessible in your system’s PATH.
  • Compilation Errors: Ensure your environment supports C++11 or later and that make is installed.

Author

Brandon Figueroa Ugalde - ID# 660282688

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