1.5.1. Basic Commands and Utilities

There are many types of shells available for Linux. The most important difference between shells is the command language. For example, the C shell (csh) uses a command language somewhat like the C programming language. The classic Bourne shell uses a different command language. One's choice of a shell is often based on the command language it provides. The shell that you use defines, to some extent, your working environment under Linux.

No matter what Unix shell you're accustomed to, some version of it has probably been ported to Linux. The most popular shell is the GNU Bourne Again Shell (bash), a Bourne shell variant. bash includes many advanced features, such as job control, command history, command and filename completion, an Emacs-like (or optionally, a vi-like) interface for editing the command line, and powerful extensions to the standard Bourne shell language. Another popular shell is tcsh, a version of the C shell with advanced functionality similar to that found in bash. Other shells include the Korn shell (ksh), BSD's ash, zsh, a small Bourne-like shell, and rc, the Plan 9 shell.

What's so important about these basic utilities? Linux gives you the unique opportunity to tailor a custom system to your needs. For example, if you're the only person who uses your system, and you prefer to use the vi editor and the bash shell exclusively, there's no reason to install other editors or shells. The "do it yourself" attitude is prevalent among Linux hackers and users.

1.5.2. Text Processing and Word Processing

In the Unix world, text processing is much more common, which is quite different from the classical concept of word processing. With a text-processing system, the author enters text using a "typesetting language" that describes how the text should be formatted. Instead of entering the text within a special word processing environment, the author may modify the source with any text editor, such as vi or Emacs. Once the source text (in the typesetting language) is complete, the user formats the text with a separate program, which converts the source to a format suitable for printing. This is somewhat analogous to programming in a language such as C, and "compiling" the document into a printable form.

Text processors such as TeX and groff differ mostly in the syntax of their formatting languages. The choice of one formatting system over another is also based upon what utilities are available to satisfy your needs, as well as personal taste.

For example, some people consider the groff formatting language to be a bit obscure, so they use TeX, which is more readable by humans. However, groff is capable of producing plain ASCII output, viewable on a terminal, while TeX is intended primarily for output to a printing device. Still, various programs exist to produce plain ASCII from TeX-formatted documents or to convert TeX to groff, for example.

Text processors are used widely in the computing community for producing papers, theses, magazine articles, and books. (In fact, this book was originally written in the LaTeX format, filtered into a home-grown SGML system, and printed from groff.) The ability to process the source language as a plain-text file opens the door to many extensions to the text processor itself. Because source documents are not stored in an obscure format, readable only by a particular word processor, programmers are able to write parsers and translators for the formatting language, thus extending the system.

<sect2><title>Basic Commands and Utilities</title>

<para>

Virtually every utility you would expect to find on standard
implementations of Unix has been ported to Linux. This
includes basic commands such as <command>ls</command>,
<command>awk</command>, <command>tr</command>,
<command>sed</command>, <command>bc</command>,
<command>more</command>, and so on.  There are Linux ports
of many popular software packages including Perl, Python,
the Java Development Kit, and more. You name it--Linux has
it.  Therefore, you can expect your familiar working
environment on other Unix systems to be duplicated on
Linux. All of the standard commands and utilities are
there.
(Novice Unix users should see
<xref linkend="X-100-3-chap-basic"> for an introduction to
these basic Unix commands.)

</para>

At first glance, the typesetting language may appear to be obscure, but it's actually quite easy to learn. Using a text-processing system enforces typographical standards when writing. For example, all enumerated lists within a document will look the same, unless the author modifies the definition of the enumerated list "environment."

The primary goal of typesetting languages is to allow the author to concentrate on writing the actual text, instead of worrying about typesetting conventions. When the example just shown is printed, the commands in <command> tags will be printed using whatever font, color, or other convention the publisher has chosen, and a command index can easily be generated too. Furthermore, the correct chapter number and title are plugged in where the strange-looking <xref&> tag was written, so they are correct even if the authors reorder the chapters after writing the paragraph.

The subtle benefit of text processing is that the system allows you to specify exactly what you mean. Also, text processing systems allow you to edit the source text with any text editor, and the source is easily converted to other formats. The tradeoff for this flexibility and power is the lack of a WYSIWYG interface.

Many users of word processors are used to seeing the formatted text as they edit it. On the other hand, when writing with a text processor, one generally doesn't worry about how the text will appear once it's formatted. The writer learns to expect how the text should look from the formatting commands used in the source.

1.5.3. Commercial Applications

1.5.4. Programming Languages and Utilities

Besides C, C++, and Java, many other compiled and interpreted programming languages have been ported to Linux, such as Smalltalk, FORTRAN, Pascal, LISP, Scheme, and Ada. In addition, various assemblers for writing machine code are available, as are Unix-hacking favorites such as Perl (the script language to end all script languages), Tcl/Tk (a shell-like command-processing system that includes support for developing simple X Window System applications), and Python (the first scripting language to be designed as object-oriented from the ground up).

With Linux, not only do you have access to the complete set of libraries and programming utilities, but you also have the complete kernel and library source code at your fingertips.

Chapters 13 and 14 are devoted to the programming languages and tools available for Linux.

1.5.5. The X Window System

One of the real strengths of the X Window System is that its "look and feel" is greatly customizable. It's possible to emulate the Windows 95/98, Macintosh, and NeXTStep environments under X, as well as to create totally novel desktop configurations (many Linux users prefer to make up their own).

Many X-specific applications have been written, such as games, graphics utilities, programming and documentation tools, and so on. With Linux and X, your system is a bona fide workstation. Coupled with TCP/IP networking, you can even display X applications running on other machines on your Linux screen, as is possible with other systems running X.

Standard X applications include xterm (a terminal emulator used for most text-based applications within an X window), xdm (the X Session Manager, which handles logins), xclock (a simple clock display), xman (an X-based manual page reader), and more. The many X applications available for Linux are too numerous to mention here, but the base XFree86 distribution includes the "standard" applications found in the original MIT release. Many others are available separately, and theoretically any application written for X should compile cleanly under Linux.

The XFree86 distribution contains programming libraries and includes files for those wily programmers who wish to develop X applications. Various widget sets, such as Athena, Open Look, and Xaw3D, are supported. All of the standard fonts, bitmaps, manual pages, and documentation are included. PEX (a programming interface for 3D graphics) is also supported, as is Mesa, a free implementation of the OpenGL 3D graphics primitives.

With KDE and GNOME, even casual users and beginners will feel right at home with Linux. Most distributions automatically configure one of these desktop environments during installation, making it unnecessary to ever touch the text-only console interface.

While both KDE and GNOME aim to make the Unix environment more user-friendly, they have different emphases. KDE's main goals are ease-of-use, stability, and user-interface compatibility with other computing environments (such as Windows 95). GNOME, on the other hand, aims more at good looks and maximum configurability.

1.5.7. Networking

Other networking features include NNTP-based electronic news systems such as C News and INN; the sendmail, exim and smail mail transfer agents; telnet, rlogin, ssh, and rsh, which allow you to log in and execute commands on other machines on the network; and finger, which allows you to get information on other Internet users. There are tons of TCP/IP-based applications and protocols out there.

If you have experience with TCP/IP applications on other Unix systems, Linux will be familiar to you. The system provides a standard socket programming interface, so virtually any program that uses TCP/IP can be ported to Linux. The Linux X server also supports TCP/IP, allowing you to display applications running on other systems on your Linux display. Administration of Linux networking will be familiar to those coming from other Unix systems, as the configuration and monitoring tools are similar to their BSD counterparts.

1.5.8. Telecommunications and BBS Software

If you do not have access to a TCP/IP network or UUCP feed, Linux allows you to communicate with a number of BBS networks, such as Fidonet, with which you can exchange electronic news and mail via the phone line.

1.5.9. Interfacing with Windows and MS-DOS

The MS-DOS emulator is still under development, yet many popular applications run under it. Understandably, however, MS-DOS applications that use bizarre or esoteric features of the system may never be supported, because it's only an emulator. For example, you wouldn't expect to be able to run any programs that use x86 protected-mode features, such as Microsoft Windows (in 386-enhanced mode, that is).

Applications that run successfully under the Linux MS-DOS Emulator include 4DOS (a command interpreter), Foxpro 2.0, Harvard Graphics, MathCad, Turbo Assembler, Turbo C/C++, Turbo Pascal, Microsoft Windows 3.0 (in real mode), and WordPerfect 5.1. Standard MS-DOS commands and utilities, such as PKZIP, work with the emulator as well.

The MS-DOS Emulator is meant mostly as an ad hoc solution for those people who need MS-DOS only for a few applications, but use Linux for everything else. It's not meant to be a complete implementation of MS-DOS. Of course, if the Emulator doesn't satisfy your needs, you can always run MS-DOS as well as Linux on the same system (but not at the same time). Using the LILO boot loader, you can specify which operating system to start at boot time. Linux can coexist with other operating systems, such as OS/2, as well.

1.5.10. Other Applications

A host of miscellaneous applications are available for Linux, as one would expect from such a hodgepodge operating system. Linux's primary focus is currently for personal Unix computing, but this is rapidly changing. Business and scientific software is expanding, and commercial software vendors are beginning to contribute to the growing pool of applications.

Of course, there are many more such applications that have been, and can be, ported to run on Linux. Whatever your field, porting Unix-based applications to Linux should be straightforward. Linux provides a complete Unix programming interface, sufficient to serve as the base for any scientific application.