PyShell

A minimal shell environment written in Python. This script provides basic shell functionalities, including built-in commands and the ability to execute external programs.

---

Features

• Built-in commands:

  • echo: Prints the given arguments to the standard output.
  • type: Displays information about a command (e.g., if it is a shell built-in or an external program).
  • pwd: Prints the current working directory.
  • cd: Changes the current directory.
  • cat: Prints the content of files to the standard output.
  • exit 0: Exits the shell.

• Executes external commands available in the system's PATH.

• Redirecting/appending of command outputs and or errors into files.

• Robust error handling for invalid commands, missing files, and permission issues.

• Graceful handling of keyboard interruptions (Ctrl+C).

Usage

Shell Commands

The shell supports the following commands:

1. echo [arguments...]

   • Prints the arguments to the terminal.
   • Example:

     $ echo Hello, World!
     Hello, World!

2. type [command]

   • Displays information about a command (e.g., whether it is a shell built-in or an external program).
   • Example:

     $ type echo
     echo is a shell builtin

3. pwd

   • Prints the current working directory.
   • Example:

     $ pwd
     /home/user

4. cd [directory]

   • Changes the current working directory. Use cd ~ to navigate to the home directory.
   • Example:

     $ cd /path/to/directory
     $ pwd
     /path/to/directory

5. cat [file...]

   • Prints the contents of one or more files to the terminal.
   • Example:

     $ cat file1.txt file2.txt
     [contents of file1.txt]
     [contents of file2.txt]

6. exit 0

   • Exits the shell.

External Commands

• You can also run any external commands available in the system PATH:

  $ ls -l
  [output of `ls -l`]

Redirection

The shell supports standard output and error redirection for commands. You can redirect the output of both built-in and external commands to files.

Standard Output Redirection

• Overwrite existing file (> or 1>):

  $ echo "Hello, World!" > output.txt

  This command will write "Hello, World!" to output.txt, overwriting any existing content.

• Append to existing file (>> or 1>>):

  $ echo "Hello, again!" >> output.txt

  This command will append "Hello, again!" to output.txt.

Standard Error Redirection

• Overwrite existing file (2>):

  $ cat non_existent_file 2> error.log

  This command will redirect the error message to error.log, overwriting any existing content.

• Append to existing file (2>>):

  $ cat non_existent_file 2>> error.log

  This command will append the error message to error.log.

Combined Standard Output and Error Redirection

• Redirect both stdout and stderr to separate files:

  $ command > output.log 2> error.log

  This redirects standard output to output.log and standard error to error.log.

Examples

1. Save command output:

   $ pwd > current_directory.txt

2. Log errors:

   $ cat missing_file.txt 2> error_log.txt

3. Append multiple outputs:

   $ echo "Line 1" >> log.txt
   $ echo "Line 2" >> log.txt

4. Save both output and errors:

   $ ls /some/path > output.log 2> errors.log

Note: The shell creates directories automatically if they don't exist when redirecting output to a file in a non-existent directory.

Installation

To install and run the Basic Shell Emulator, follow these steps:

1. Clone the repository

• Clone the repository to your local machine using Git:

  git clone https://github.com/LogicalGuy77/py-shell.git
  cd py-shell

2. Run the shell emulator

• Once you turn on WSL ( if on windows ), you can run the shell emulator using the provided py_shell.sh script. This script will execute the Python code:

  ./py_shell.sh

4. (Optional) Running the shell without py_shell.sh

• If you don't want to use the py_shell.sh script, you can run the Python script directly by using:

  cd .\app\
  python main.py

5. Additional Notes

• Platform Compatibility: The shell should work on Linux and macOS. MacOS users may need to adjust the script execution process to ensure compatibility with their environment.

• Permissions: Ensure that the mini-shell.sh script is executable. If not, you can make it executable using:

  chmod +x py_shell.sh

Acknowledgments

This project was built as part of the Codecrafters challenge, with all implementation done independently.