Several GNU utilities share the options listed in Table V-2. The utilities that use these options are marked as such.
Table V-2. Common command line options
A single hyphen appearing in place of a filename indicates that the utility will accept standard input in place of the file.
A double hyphen marks the end of the options on a command line. You can follow this option with an argument that begins with a hyphen. Without this option the utility assumes that an argument that begins with a hyphen is an option.
Displays a help message for the utility. Some of these messages are quite long; you can pipe the output through less to display it one screen at a time. For example, you could give the command ls help | less. Alternatively you can pipe the output through grep if you are looking for specific information. For example, you could give the following command to get information on the d option to ls: ls help | grep d. See the preceding entry in this table for information on the double hyphen.