Conventions Used in This Book

This book uses conventions to make its explanations shorter and clearer. The following paragraphs describe these conventions.

Text and examples

The text is set in this type, whereas examples are shown in a monospace font (also called a fixed-width font):

 $ cat practice This is a small file I created with a text editor. 

The next paragraph explains why part of the first line is in a bold typeface.

Items you enter

Everything you enter at the keyboard is shown in a bold typeface: Within the text, this bold typeface is used; within examples and screens, this one is used. In the previous example, the dollar sign ($) on the first line is a prompt that Linux displays, so it is not bold; the remainder of the first line is entered by a user, so it is bold.

Utility names

Names of utilities are printed in this bold sans serif typeface. This book references the emacs editor and the ls utility or ls command (or just ls), but instructs you to enter ls a on the command line. The text distinguishes between utilities, which are programs, and the instructions you give on the command line to invoke the utilities.

Filenames

Filenames appear in a bold typeface. Examples are memo5, letter.1283, and reports. Filenames may include uppercase and lowercase letters; however, Linux is case sensitive (866), so memo5, MEMO5, and Memo5 name three different files.

Character strings

Within the text, characters and character strings are marked by putting them in a bold typeface. This convention avoids the need for quotation marks or other delimiters before and after a string. An example is the following string, which is displayed by the passwd utility: Sorry, passwords do not match.

Keys and characters

This book uses SMALL CAPS for three kinds of items:

• Important keyboard keys, such as the SPACE bar and the RETURN,^[1] ESCAPE, and TAB keys.

  ^[1] Different keyboards use different keys to move the cursor (870) to the beginning of the next line. This book always refers to the key that ends a line as the RETURN key. Your keyboard may have a RET, NEWLINE, Enter, RETURN , or other key. Some keyboards have a key with a bent arrow on it. (The key with the bent arrow is not an arrow key. Arrow keys have straight shafts.) Use the corresponding key on your keyboard each time this book asks you to press RETURN.

• The characters that keys generate, such as the SPACEs generated by the SPACE bar.

• Keyboard keys that you press with the CONTROL key, such as CONTROL-D. (Even though D is shown as an uppercase letter, you do not have to press the SHIFT key. Enter CONTROL-D by holding down the CONTROL key and pressing d.)

Prompts and RETURNs

Most examples include the shell prompt the signal that Linux is waiting for a command as a dollar sign ($). The prompt is not in boldface, because you do not enter it. Do not type the prompt on the keyboard when you are experimenting with examples from this book. If you do, the examples will not work.

Examples omit the RETURN keystroke that you must use to execute them. An example of a command line is

 $ vim memo.1204 

To use this example as a model for running the vim editor, give the command vim memo.1204 and press the RETURN key. (Press ESCAPE ZZ to exit from vim; see page 141 for a vim tutorial.) This method of entering commands makes the examples in the book correspond to what appears on your screen.

Definitions

All entries marked with ^FOLDOC are courtesy of Denis Howe, editor of the Free Online Dictionary of Computing (www.foldoc.org), and are used with permission. This site is an ongoing work containing not just definitions but also anecdotes and trivia.

optional

Passages marked as optional are not central to the ideas presented in the chapter but often involve more challenging concepts. A good strategy when reading a chapter is to skip the optional sections and then return to them when you are comfortable with the main ideas presented in the chapter. This is an optional paragraph.

URLs (Web addresses)

Web addresses, or URLs, have an implicit http:// prefix, unless ftp:// or https:// is shown. You do not normally need to specify a prefix when the prefix is http://, but you must use a prefix from a browser when you specify an FTP or secure HTTP site. Thus you can specify a URL in a browser exactly as shown in this book.

Tip, Caution, and Security boxes

The following boxes highlight information that may be helpful while you are using or administrating a Linux system.

tip: This is a tip box

A tip box may help you avoid repeating a common mistake or may point toward additional information.

caution: This box warns you about something

A caution box warns you about a potential pitfall.

security: This box marks a security note

A security box highlights a potential security issue. These notes are usually for system administrators but some apply to all users.