A.6. Shell Clones and Unix-like Platforms

The proliferation of shells has not stopped at the boundaries of UNIX-dom. Many programmers who got their initial experience on UNIX systems and subsequently crossed over into the PC world wished for a nice UNIX-like environment. It's not surprising then that several UNIX shell-style interfaces to small-computer operating systems have appeared, Bourne shell emulations among them.

In the past several years, not only shell clones have appeared, but entire Unix "environments." Two of them use shells that we've already discussed. Two others provide their own shell reimplementations. Providing lists of major and minor differences is counterproductive. Instead, this section describes each environment in turn (in alphabetical order), along with contact and Internet download information.

A.6.1. Cygwin

Cygnus Consulting (now part of Red Hat) created the cygwin environment. First creating cgywin.dll, a shared library that provides Unix system call emulation, they ported a large number of GNU utilities to various versions of Microsoft Windows. The greatest functionality comes under Windows/NT, Windows 2000, and Windows XP, although the environment can and does work under Windows 95/98/ME, as well.

The cygwin environment uses bash for its shell, GCC for its C compiler, and the rest of the GNU utilities for its Unix toolset. A sophisticated mount command provides a mapping of the Windows C:\path notation to Unix filenames.

The cygwin project can be found at http://www.cygwin.com.

A.6.2. DJGPP

The DJGPP suite provides 32-bit GNU tools for the MS-DOS environment. To quote the web page:

DJGPP is a complete 32-bit C/C++ development system for Intel 80386 (and higher) PCs running MS-DOS. It includes ports of many GNU development utilities. The development tools require a 80386 or newer computer to run, as do the programs they produce. In most cases, the programs it produces can be sold commercially without license or royalties.

The name comes from the initials of D.J. Delorie, who ported the GNU C++ compiler, g++ to MS-DOS, and the text initials of g++, GPP. It grew into essentially a full Unix environment on top of MS-DOS, with all the GNU tools and bash as its shell. Unlike cygwin or UWIN (see later in this Appendix), you don't need a version of Windows, just a full 32-bit processor and MS-DOS. (Although, of course, you can use DJGPP from within a Windows MS-DOS window.) The web site is http://www.delorie.com/djgpp/.

A.6.3. MKS Toolkit

Perhaps the most established Unix environment for the PC world is the MKS Toolkit from Mortice Kern Systems:

MKS Canada - Corporate Headquarters

410 Albert Street

Waterloo, ON  N2L 3V3

Canada

+1 519 884-2251

+1 519 884-8861 (fax)

+1 800 265-2797 (sales)

http://www.mks.com

The MKS Toolkit comes in various versions depending upon the development environment and the number of developers who will be using it. It includes a shell that is POSIX-compliant, along with just about all the features of the 1988 Korn shell, as well as over 300 utilities, such as awk, perl, vi, make, etc. Their library supports over 1,500 Unix APIs, making it extremely complete and easy to port to the Windows environment. More information is available at http://www.mkssoftware.com/products/tk/ds_tkdev.asp.

A.6.4. AT&T UWIN

The UWIN package is a project by David Korn and his colleagues to make a Unix environment available under Microsoft Windows. It is similar in structure to cygwin, discussed earlier. A shared library, posix.dll, provides emulation of the Unix system call APIs. The system call emulation is quite complete. An interesting twist is that the Windows registry can be accessed as a filesystem under /reg. On top of the Unix API emulation, ksh93 and over 200 Unix utilities (or rather, re-implementations) have been compiled and run. The UWIN environment relies on the native Microsoft Visual C/C++ compiler, although the GNU development tools are available for download and use with UWIN.

The project can be found at http://www.research.att.com/sw/tools/uwin/. The web site describes what is available, with links for downloading binaries, as well as information on commercial licensing of the UWIN package. Also included are links to various papers on UWIN, additional useful software, and links to other, similar packages.