Conventions Used in This eBook

The following typographic conventions are used in this tutorial:

• Italic
• is used for names, including pathnames, filenames, program and command names, usernames, hostnames, machine names, and mailing-list names, as well as for mail addresses. It is also used to emphasize new terms and concepts when they are introduced.
• Constant Width
• is used in examples to show the contents of files or the output from commands. This includes examples from the configuration file or other files such as message files, shell scripts, or C language program source. Constant-width text is quoted only when necessary to show enclosed space; for example, the five-character "From " header.

  Single characters, symbolic expressions, and command-line switches are always shown in constant-width font. For instance, the o option illustrates a single character, the rule $- illustrates a symbolic expression, and -d illustrates a command-line switch.

• Constant Bold
• is used in examples to show commands or some other text that is to be typed literally by the user. For example, the phrase cat/etc/sendmail.pid means the user should type "cat/etc/sendmail.pid" exactly as it appears in the text or example.
• Constant Italic
• is used in examples to show variables for which a context-specific substitution should be or will be made. In the string Snum, for example, num will be a user-assigned integer. In the output error: num, for example, num will be a variable value printed by a program (usually sendmail).
• %
• indicates a user shell.
• #
• indicates a root shell.