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| Preface |

## Format

The following sections describe the conventions used in this handbook.

### Commands

We introduce each main concept, then break it down into task-oriented sections. Each section shows the best command to use for a task, explains what it does, and the syntax (the way to put the command line together). The syntax is given like this:

> rm filename

Commands appear in boldface type (in this example, rm). You should type the command exactly as it appears in the example. The variable parts (here, filename) will appear in italic type; you must supply your own value. To enter this command, you would type rm followed by a space and the name of the file that you want to remove, then press the `[RETURN]` key. (Your keyboard may have a key labeled `[ENTER]`, or an arrow with a right-angle shaft, instead of a `[RETURN]` key.) Throughout this book, the term enter means to type a command and press `[RETURN]` to run it.

### Examples

Examples show what should happen as you enter a command. Some examples assume that you've created certain files. If you haven't, you may not get the results shown.

We use typewriter-style characters for examples. Items you type to try the example are `boldface`. System messages and responses are `normal text`.

Here's an example:

>     % date
>     Tue Nov  4 13:39:24 EST 1997
>     %

The character "%" is the shell (system) prompt. To do this example, you would type date and then press `[RETURN]`. The date command responds "Tue Nov 4 13:39:24 EST 1997" and then returns you to the prompt.

### Problem Checklist

We've included a problem checklist in some sections. You may skip these parts and go back to them if you have a problem.

### Exercises

Many sections have exercises to reinforce the text you've read. Follow the exercises, but don't be afraid to experiment on your own.

The exercises have two columns: the left-hand column tells you what to do and the right-hand column tells you how to do it. For example, a line in the exercise near the end of Chapter 1, Getting Started , shows:

Get today's date | Enter `date`

To follow the exercise, you type in the word date on your keyboard and then press the `[RETURN]` key. The left-hand column tells you what will happen.

After you try the commands, you'll have a better idea of the ones you want to learn more about. You can then look them up in your system's UNIX documentation or use one of the other references listed in Appendix A.

### A Note to Our Readers

We update each book periodically. This allows us to incorporate changes suggested to us by our readers. We'd like new users to benefit from your experience as well as ours.

If you have a suggestion, or solve a significant problem that our handbook does not cover, please write to or call us at the following address and let us know about it (include information about your UNIX environment and the computer you use):

> O'Reilly & Associates, Inc.
> 101 Morris Street
> Sebastopol, CA 95472
> 1-800-998-9938 (in US or Canada)
> 1-707-829-0515 (international/local)
> 1-707-829-0104 (FAX)

If you have access to electronic mail (Chapter 3, Your UNIX Account ), you may email your comments to:

> bookquestions@oreilly.com

You'll have our thanks, along with thanks from future readers of this handbook.

What's New in the Fourth Edition |  | Acknowledgments