The following conventions are used in this book:
Italic is used for UNIX file, directory, user, command, and group names and for system calls, passwords, and URLs. It is also used to emphasize new terms and concepts when they are introduced.
Constant Width is used for code examples and any system output.
Constant Width Italic is used in examples for variable input or output (e.g., a filename).
Constant Width Bold is used in examples for user input.
Strike-through is used in examples to show input typed by the user that is not echoed by the computer. This is mainly used for passwords and passphrases that are typed.
call ( ) is used to indicate a system call, in contrast to a command. In the original edition of the book, we referred to commands in the form command (1) and to calls in the form call (2) or call (3), where the number indicates the section of the UNIX programmer's manual in which the command or call is described. Because different vendors now have diverged in their documentation section numbering, we do not use this convention in this second edition of the book. (Consult your own documentation index for the right section.) The call ( ) convention is helpful in differentiating, for example, between the crypt command and the crypt ( ) library function.
% is the UNIX C shell prompt.
$ is the UNIX Bourne shell or Korn shell prompt.
# is the UNIX superuser prompt (Korn, Bourne, or C shell). We usually use this for examples that should be executed by root.
Normally, we will use the Bourne or Korn shell in our examples unless we are showing something that is unique to the C shell.
[ ] surround optional values in a description of program syntax. (The brackets themselves should never be typed.)
CTRL-X or ^X indicates the use of control characters. It means hold down the CONTROL key while typing the character "X."
All command examples are followed by RETURN unless otherwise indicated.