This book uses the following typographical conventions:


Is used for the names of files, directories, hostnames, domain names, and URLs, and to emphasize new terms when they are first introduced.


Is used to show the contents of files, command syntax, and the output from commands.


Is used in examples to show variables for which a context-specific substitution should be made. (The variable filename, for example, would be replaced by some actual filename.)

[ option ]

When showing command syntax, we place optional parts of the command within brackets. For example, ls [-l] means that the -l option is not required.

This is an example of a Note. Notes are short asides that convey supplemental information that may not be important to all readers.

This is an example of a Warning. Warnings highlight dangerous procedures?those that may damage you, your hardware, or your data. Disregard warnings at your own peril.