Learning the Korn Shell

Appendix A. Related Shells

The fragmentation of the UNIX marketplace has had its advantages and disadvantages. The advantages came mostly in the early days: lack of standardization and proliferation among technically savvy academics and professionals contributed to a healthy “free market” for UNIX software, in which several programs of the same type (e.g., shells, text editors, system administration tools) would often compete for popularity. The best programs would usually become the most widespread, while inferior software tended to fade away.

But often there was no single “best” program in a given category, so several would prevail. This led to the current situation, where multiplicity of similar software has led to confusion, lack of compatibility, and-most unfortunate of all-UNIX’ inability to capture as big a share of the market as other operating platforms (MS-DOS, Microsoft Windows, Novell NetWare, etc.).

The “shell” category has probably suffered in this way more than any other type of software. As we said in the Preface and Chapter 1, of this book, several shells are currently available; the differences between them are often not all that great. We believe that the Korn shell is the best of the most widely used shells, but other shells certainly have their staunch adherents, so they aren’t likely to fade into obscurity for a while.

Therefore we felt it necessary to include information on shells similar to the 1988 UNIX Korn shell. This Appendix summarizes the differences ...