3.3 Important Cisco IOS Features
3.3.2 Using the help feature

The help command on a Cisco IOS command-based switch works the same as that on a router. On a switch, you access help by entering ? on a command line. The switch then prompts you with all possible choices for the next parameter. If you type in the next parameter and type ? again, the switch displays the next set of command-line choices. In fact, the switch displays help on a parameter-by-parameter basis. Additionally, when the switch displays help options, it also ends by displaying the portion of the command that you entered so far. This enables you to continue to append commands to the line without needing to reenter the previous portion of the command.

The help system on a set command-based switch functions differently from the router. You access help in the same manner as you do in a router, but the results differ. For example, where a router prompts you for the next parameter, the Catalyst switch displays the entire usage options for the command. Figure shows the help result for a partial command string. The string does not uniquely identify what parameter should be modified and lists all related commands.

On the other hand, if you have enough of the command on the line that the Catalyst switch recognizes what command you intend to implement, it displays the options for that command. This time, in Figure , the string identifies a specific command and the Catalyst switch displays help appropriate for that command. The user here wants to modify the console interface in some way, but is unsure of the syntax used with the command.

Notice that when the console displays help, it returns the command line with a blank line. The command string you entered so far is not displayed for you as it is on a router. You can now use command recall. Suppose you want to disable the logical interface, sc0. So you want to enter the command set int sc0 down. You decide to use command recall and complete the command. What happens if you type !! sc0 down ? You see the command usage screen again, without the console changing state to down. This happens because the command recall executes the previous statement that was set int ? with the help question mark and your appended parameters. When you add the additional parameters, the switch interprets the string as set int ? sc0 down, sees the question mark, and displays help.