meta.sh

A tiny shell for Linux, implemented in C++, written as part of my Operating Systems Lab course!

Features

Builtins

The shell has support for the following builtins

• cd - Change the working directory
• pwd - Pring the current working directory
• help - Show a help menu (As shown in the image)
• exit - Cleanly exit the shell
• fetch - Show system information
• history - Show all commands executed on the shell
• setenv - Set an environment variable to specified value
• getenv - Fetch the value of the given environment variable
• unsetenv - Unset the given environment variable

Running External Commands

The shell can run executables present in the users PATH. You can execute using the name of the executable or specify the full path

Running in background

Processes can be run in background by adding & at the end of the input. The shell will prompt the next input instead of waiting for the command to finish

I/O Redirection

Use the < symbol to redirect input from a file and the > symbol to redirect output to a file. Implemented using the dup2() system call. For example:

ls > out.txt
./a.out < in.txt > out.txt

Piping

There is support for pipes between commands (Any number of pipes), using the pipe() system call. For example:

ls | more
cat file.txt | grep "somestring" | wc -l > out.txt

Installation/Usage

meta.sh uses the GNU Readline library to add support for history and editing. Please install the library (Called libreadline6-dev on Debian and derivatives)

After cloning the source code, running make will build and generate an exectuable called shell

git clone https://github.com/mukul-mehta/meta.sh.git
cd meta.sh
make
./shell

TODOs

• Support reading and writing history to a file, using GNU Readline functions

• Add support for setting and unsetting environment variables

• Add support for aliases

• Migrate to C. We aren't really using any C++ features, other than vectors

• Support macOS - For now, using some Linux specific headers to fetch sysinfo