The IOS has several forms of help available:

Context-Sensitive Help

The context-sensitive help provides a list of commands and the arguments associated with those commands within the context of the current mode. To access context-sensitive help, enter a question mark, ?, at any prompt. There is an immediate response without the need to use the Enter key.

One use of context-sensitive help is to get a list of available commands. This can be used when you are unsure of the name for a command or you want to see if the IOS supports a particular command in a particular mode.

For example, to list the commands available at the user EXEC level, enter a question mark, ?, at the Switch> prompt.

Another use of context-sensitive help is to display a list of commands or keywords that start with a specific character or characters. After entering a character sequence, if a question mark is immediately entered, without a space, the IOS will display a list of commands or keywords for this context that start with the characters that were entered.

For example, enter sh? to get a list of commands that begins with the character sequence sh.

A final type of context-sensitive help is used to determine which options, keywords, or arguments are matched with a specific command. When entering a command, enter a space followed by a ? to determine what can or should be entered next.

As shown in the figure, after typing the command clock set 19:50:00, we can enter the ? to determine the additional options or keywords available for this command.