Help can actually be used in different ways. We’ve already seen that leaving a space after a command and then entering the question mark provides us with a list of the possible commands that are expected next. However, the question mark can also be used as a type of lookup character. For example, entering a letter or series of letters directly followed by the question mark (no space) provides a list of commands that start with those characters. Consider the output from entering c?.
toronto-1#c?
cd clear clock configure connect
copy
This provides a list of all of the commands starting with the letter C that are available from the current prompt. Going a step further, you could enter the first two (or more) letters directly followed by the question mark. In this case, let’s enter cl?.
toronto-1#cl?
clear clock
This time, the only commands listed are those starting with the letters CL. Using the help command will also give you an idea of how truncated a command can be without being considered ambiguous. For example, it should be obvious that entering only cl would not be enough to use as a shortcut for clock, since the router won’t know whether we had meant to enter clock or clear. Add one additional letter, however, and we have a unique entry.
toronto-1#clo
% Incomplete command.
Notice what just happened – the router recognizes that I’m entering the clock command, but tells me that it’s incomplete. Stepping back to what you just learned, you could find out more about the additional commands required by the clock command by entering clo ?.
toronto-1#clo ?
set Set the time and date
Don’t be bashful. Whether on an exam or in real life, there is never anything wrong with using the help commands. If you’re ever in doubt, just remember that the help feature is there for a purpose – nobody can remember everything!
