Using Command Completion; Entering Abbreviated Commands; Negating Commands - Dell PowerEdge M420 Configuration Manual

You can also enter a question mark (?) after typing one or more characters of a
word to list the available command or parameters that begin with the letters,
as shown in the following example:
console#show po?
policy-map port ports

Using Command Completion

The CLI can complete partially entered commands when you press the
<Tab> or <Space> key.
console#show run<Tab>
console#show running-config
If the characters you entered are not enough for the switch to identify a single
matching command, continue entering characters until the switch can
uniquely identify the command. Use the question mark (?) to display the
available commands matching the characters already entered.

Entering Abbreviated Commands

To execute a command, you need to enter enough characters so that the
switch can uniquely identify a command. For example, to enter Global
Configuration mode from Privileged EXEC mode, you can enter con instead
of configure.
console#con
console(config)#

Negating Commands

For many commands, the prefix keyword no is entered to cancel the effect of
a command or reset the configuration to the default value. All configuration
commands have this capability.
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Using the Command-Line Interface