Quantum Shell - A basic shell by Juan and Depanshu

Quantum Shell is a very basic shell made in C. It has the following functionalities:

• N-stage pipelining: Supports chaining multiple commands using pipes (|)
• I/O redirection: Supports Input(<) and Output(>) redirection
• Command search pathways: Searches system paths for commands (e.g., ls -l works), but arguments like file paths still need to be fully specified (e.g., ls /path/to/some_file)
• Built in cd command: Allows changing of directories
• Basic Signal handling: Ctrl C is ignored for the current shell process. SIGCHLD for proper background process and cleanup.

Installation

The build directory already has the executable - quantum_shell. Otherwise, run the makefile

Usage

//List the directories
QuantumShell$$: ls -l

// Output to the file 
QuantumShell$$: ls -l > out.txt

// Change the working directory to parent
QuantumShell$$: cd ..

// Multi Stage pipelining
QuantumShell$$: grep #include | sort < headers/cmd_runner.h

Testing - Test cases are included in final_tst.md file

Syntax

The Syntax cam ne described in terms of a CFG :
Job → Pipeline [< token] [> token] [&]
Pipeline → Command [| Pipeline]
Command → Args
Args → token [Args]

Above:
- The '<', '>', '&' and | are terminal symbols. Token represent any sequence of non-whitespace characters.
- Square brackets indicate an optional segment

Known bugs and limitations

Quotes (' ' / " ")	Programs like `awk` and `grep` don't work with arguments enclosed in quotes. Instead of `grep "#include"`, use `grep #include`. Since the tokenizer treats each word separated by whitespace as a single token, unlike bash, this shell can't treat multiple words as a single token
Environment variable expansion	The shell does not support environment variable expansion. For example, `echo $PATH` will not expand "PATH".

References

THe syntax description was taken from our teacher, Mark Shroeder's guidance document