CISCO IOS in a Nutshell

Command-Line Completion

Command-line completion makes the IOS interface much more user-friendly. It saves you extra typing and helps out when you cannot remember a command’s syntax. In a previous example, we used the command configure terminal:

Router#configure terminal

But you could have saved wear and tear on your hands by typing:

Router#conf t

IOS expands the command conf t to configure terminal. Another shortcut is to press Tab after typing “conf”; the router will fill in the best completion, which is “configure”. Here is another example:

Router#show running-config

This long command can be shortened to:

Router#sh ru

The router knows that “show” is what you wanted because show is the only command that begins with “sh”; likewise, the only subcommand of show that begins with “ru” is running-config.

If the router does not understand a command, it repeats the entire command line and places a caret (^) under the point at which it ran into trouble. For example:

Router>show itnerface e0
>show itnerface e0
       ^
% Invalid input detected at '^' marker.

The caret symbol is pointing to the “t” in “itnerface”, which is the command the router does not understand. We can quickly fix that by retyping the command:

Router>show interface e0

We now get the correct output! Since we also know how to use shortcuts, we can type:

Router>sh int e0

With this command we get the same result as its lengthy counterpart. Command-line completion saves a lot of typing, and it helps you keep your sanity when you’re working with long commands.

Another form of command-line completion is the use of the Tab key. If you start a command by entering the first few characters, you can hit the Tab key. As long as there is only one match, the router will complete the command: for example, if you type “sh” and hit Tab, the router completes the “sh” with “show”. If the router does not complete the command, you can enter a few more letters and try again.