phipsshell - a simple bash-like shell written in C++

About

I had to write a shell for an uni project a few semesters ago. I did this in C and the outcome was quite interesting. I learned a lot about pipes, file descriptors, fork, exec, and some other UNIX facilities. I wanted to revive this project and open source it to keep the learnings in my memory and to share them with other people facing this task. So I took the code from then and rewrote ugly parts in C++.

Focus is educational and for personal experience - not a production-ready shell!

Code and code quality

I'm not an experienced C++ developer. My testing so far (valgrind) shows I have no memory leaks and the overall code quality looks at least "okay" to me. At least the important parts! The parsing and validation stuff is not really solid, tho. But I spend some time into making the actual execution and Pipe creation + handling nice.

Important parts of code: See action.cpp: action_command() and pipe.class.cpp: Pipe().

Functionality

This shell focuses on proper user input! Validation is only very coarse-grained and definitely not bullet-proof! The focus here is on understanding pipes and not in writing a good parser. Only single spaces are allowed and no quote marks! echo "foo bar" won't work.

Valid inputs are (subset of bash):

simple commands

• cat file.txt
• /usr/bin/cat file.txt
• ./mybin file.txt

pipes

• cat file.txt | wc -l

I/O redirection

• cat < in.txt
• cat in.txt > out.txt
• cat < in.txt | wc -l > out.txt
• cat < in.txt > out.txt doesn't work because my whole parsing code is not that good

all in combination

• cat in.txt | grep -i foo | wc -l > out.file

How to use/build phipsshell?

Runs on UNIX systems, like Linux distributions or Mac OS.

Linux (Debian, Ubuntu)

• $ sudo apt install libreadline-dev
• $ make && ./phipsshell

Mac OS

• $ brew install readline (installs only the runtime library, not the header files; therefore the header files are in ./include)
• $ make && ./phipsshell

Important parts of code

See action.cpp: action_command() and pipe.class.cpp: Pipe().

Why Makefile and CMakeLists.txt?

At the begin there was only the makefile. Because I wanted to use Jetbrains CLion I also added a CMakeLists.txt. Both files works fine. I keep the Makefile because I think it's 'nice' and I don't want to loose it.

Dependencies

phipsshell uses libreadline. Readline is distributed under a GPL v3 License. This repository contains a few header files (copied from the original source) in order to support compiling on MacOS. That is because brew install readline doesn't install header files.

Important Keywords for used UNIX facilities

• pipes, file descriptors, waitpid, WNOHANG, dup2