42sh is a bash-style shell we developped at school in C. It was a 4 weeks project, with 5 team members, even though all were not as fervent we, JC and I, were. EPITA is one of the leading Computer Science Engineering School in France, and make us learn low-level stuff (including some asm) to allow us understand deeply what's going on under the hood.
Recently, an EPITA assistant contacted me requesting that I put this code offline. As I believe in an open world where information can flow freely, I denied his censorship request. Open Source code is a fabulous way to educate, and I learnt myself a lot reading the source code of frameworks and libraries. This project was a student project and therefore is far from being quality code. Though, take it as it is. Good or bad code is good to read, to learn what to do and what not to. When I was an EPITA student, I was asked to work on Java EE, SVN, and other bunch of completely outdated technologies, it was only thank to the openness of today's internet that I could, myself, learn today's technologies. So if you're a student working on a similar project, please use this carefully. Get inspiration, but don't copy/paste without thinking! And learn by yourself, on internet! Thanks!
The boldest instruction was: "If you leak, you're dead, even for one leak". Valgrind was their witness. We hacked night and day to make our shell work, from old-style dirty parsing (Bison, Flex, Lex, Yacc, even Regex libraries were forbidden), to AST building and interpreting. Though, the last weekend, we had 2 leaks left, in the very edge case where the user would quit badly the shell. And we weren't sure whether we missed some other cases, and would loose pride with even one nasty leak.
So JC and I decided to write mmalloc (yes, malloc with 2 m, like mittsh-malloc). It also had mfree, mcalloc and mrealloc, and worked exactly as the original library functions. Except something. It kept a linked-list of pointers to all allocations. So when in need, we just had to call mmalloc_free, the magic function we documented as Frees all the managed heap..
We added some calls to signal, and catching all including SIGTERM, to free the heap even if we crash!
In fact, the day of presentation, the jury asked us dubiously So, is there any leak?, JC answered very convinced No leak. The dude inisted Are you - really - sure?. We confirmed. After running their Valgrind-based test suite, the jury had to admit: Nice, you're the first team today saying No Leak, and actually not having any.. That was our humble way to beat the system.
See mmalloc here.
I just wrote this README.md to tell the story behing 42sh, but you can checkout the original 80' style one.
All work done at EPITA, is the property of EPITA. Though, nobody asked not to open source it.