Get help in IOS

You can use the question mark to display a list of commands available in the prompt you are in:

Router#?
Exec commands:
  <1-99>      Session number to resume
  auto        Exec level Automation
  clear       Reset functions
  clock       Manage the system clock
  configure   Enter configuration mode
  connect     Open a terminal connection
  copy        Copy from one file to another
  debug       Debugging functions (see also 'undebug')
  delete      Delete a file
  dir         List files on a filesystem
  disable     Turn off privileged commands
  disconnect  Disconnect an existing network connection
  enable      Turn on privileged commands
  erase       Erase a filesystem
  exit        Exit from the EXEC
  logout      Exit from the EXEC
  mkdir       Create new directory
  more        Display the contents of a file
  no          Disable debugging informations
  ping        Send echo messages
  reload      Halt and perform a cold restart
 --More-- 

If the output spans more than one page, press the spacebar to display the following page of commands, or press Enter to go one command at a time. To quit the output, press q.

To display only commands that start with a particular character or a string of characters, type the letters and then press the question mark:

Router#de?
debug  delete  

In the picture above you can see that we’ve displayed all commands that start with de.

If the command is more than one word long, you can use the question mark to display the next command in a string:

Router#debug ?
  aaa           AAA Authentication, Authorization and Accounting
  custom-queue  Custom output queueing
  eigrp         EIGRP Protocol information
  frame-relay   Frame Relay
  ip            IP information
  ipv6          IPv6 information
  ntp           NTP information
  ppp           PPP (Point to Point Protocol) information
  standby       Hot Standby Router Protocol (HSRP)

Router#debug eigrp ?
  fsm      EIGRP Dual Finite State Machine events/actions
  packets  EIGRP packets

In the picture above you can see that we’ve displayed all commands that can follow the command debug. We then displayed all commands that can follow the commands debug eigrp.

You can also autocomplete a command. Just type the first few characters and press Tab. If there is only a single match, IOS will complete the command.

You don’t have to type an entire word to finish a command. Just can type just the first letter or a couple of letters, and if there is only a single match, IOS will understand what are you trying to accomplish. For example, you can type sh ip int b instead of the longer version, show ip interface brief:

Router#sh ip int b
Interface              IP-Address      OK? Method Status                Protocol 
GigabitEthernet0/0     unassigned      YES NVRAM  administratively down down 
GigabitEthernet0/1     unassigned      YES NVRAM  administratively down down 
GigabitEthernet0/2     192.168.0.1     YES manual up                    down 
Vlan1                  unassigned      YES NVRAM  administratively down down

Note that we were able to execute the command above because each set of characters had only one match in the list of commands. If we’ve typed sh ip in b instead, IOS would not have understood our intention:

Router#sh ip in b
% Ambiguous command: "sh ip in b"

The % Ambiguous command: “show ip in b” message was displayed because the third keyword, in, has more than one meaning (inspect or interface).


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