Layla shell is a GNU/Linux shell that includes features borrowed from bash, ksh, tcsh and zsh (to a lesser extent). Layla shell aims to implement the full functionality specified in the POSIX Shell & Utilities volume. This volume describes the Shell Command Language, the general terminal interface, and the builtin utilities of compliant shells. The full POSIX standard is freely available from The Open Group's website at:

https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/

Layla shell implements most of the POSIX-defined functionality. Specifically, quoting, token recognition, words expansions, I/O redirection, reponses to error conditions, the shell command language, the standard shell execution environment, signal handling, and the general and special builtin utilities are all implemented and behave in a way that is conforming to the POSIX standard. Pattern matching and pathname expansion relies on external tools, and thus might not behave exactly as specified in the POSIX standard. The shell grammar has been extended to accommodate some of the widely used non- POSIX words, such as the function and [[ keywords, and the (( )) arithmetic expansion operator. In all of these situations, if one or more of the major Unix shells disagreed in some aspect of their behaviour, we opted to follow ksh, as ksh is the "model" POSIX shell, the one upon which the Shell & Utilities volume was modeled in the first place. But ksh is not the only shell out there. This is why we included features from other shells, most notably bash, the most widely used shell nowadays.

There is still a long way to go with testing, bug-fixing and improving Layla shell, and your feedback is more than welcome in this regard. If you have a bug report, or you want to suggest adding some feature or fixing something with the shell, feel free to email me directly at my email address, the one you will find in the beginning of this file. If you have any bugfixes, patches or feature improvements you want to add to the code, feel free to send me your code.

Layla shell has very few external dependencies, in order to ease the process of compiling and installing it. You only need to have the GNU C library installed, in addition to the GNU Compiler Collection (GCC) or the Clang/LLVM compiler.

If you are using any GNU/Linux distro, it would be better if you checked your distro's official repositories, as these tools are installed by default on most systems. If, by a sore chance, you needed to manually download and install them, here are the links:

• GNU C Library: https://www.gnu.org/software/libc/
• GCC: https://gcc.gnu.org/
• LLVM: http://releases.llvm.org/download.html

If you downloaded the shell as a source tarball, navigate to the directory where you downloaded the tarball:

$ cd ~/Downloads

then extract the archive and enter the extracted directory:

$ tar xvf lsh-1.0
$ cd lsh-1.0/

then run:

$ make && su -c "make install"

and that's it! Now you can run the shell by invoking:

$ lsh

For more information, please read the manpage and info page in the docs/ directory.

Thanks!