This tutorial explains Cisco IOS help commands in detail with examples including context sensitive help feature.
Cisco IOS has several built in help features that will make your configuration and management task easier. Unique context sensitive help features make Cisco IOS most user friendly operating system. IOS includes thousands of possible commands and parameters, knowing how to get help can save your day.
This tutorial is third part of our article “Cisco Internetworking Operating System (IOS) Explained with Examples”. Other parts of this article are available here.
This tutorial is first part of this article. In this part, I explained naming convention used in Cisco IOS. Cisco IOS name contains a lot of information about IOS such as features, type, version, platform, compression and location.
This tutorial is second part of this article. In this part, I explained Cisco IOS mode in detail with example. Different modes are used for different purpose. This tutorial will help you in choosing correct mode for assigned task.
This tutorial is last part of this article. In this part, I will explain how to take backup of Cisco IOS step by step. Later I will explain how to restore IOS from backup to deal with unwanted situations.
In this tutorial I will explain the help features of Cisco IOS including command abbreviation, how to get help on commands and their specific parameters and recalling commands.
Context Sensitive Help
When it comes to get help on IOS command line, ? ( question mark key) stands on top of the list. It lists all possible commands starting from letters you have entered in command prompt. You can use this context sensitive help in many ways. IOS offers two type of context sensitive help:
- Word help
- Command syntax help
Word help : Word help can be used to obtain a list of commands that begin with a given letter. You know the starting letters of command, type those along with ? at command prompt and prompt will return with all matching commands. For example, we know that our command start with e. Type e? will list all commands that start with letter e.
Take another example where we completely forgotten the command . Type ? at the command prompt and hit enter key to list the all available commands.
Command syntax help : Command syntax help can be used to get the list of keyword, commands, or parameters that are available starting with the keywords that we had already entered. Enter a ? after hitting a space and router will return with the list of available command options. You can also use ? to know the required parameters for a command. For example to know the parameters required by show ip command type show ip ? and prompt will return with all associate parameters. If prompt returns with <CR> only as option, that means router does not need any additional parameters to complete the command. You can execute the command in current condition.
Space play a significant role in context sensitive help.
- To find the arguments or parameters that start with the certain word, use word and question mark with a space between them.
- To find the commands that start with certain letters, use the letters and question mark without including any space between them.
Command abbreviation and auto completion
Another cool feature offered by IOS is command abbreviation and auto completion. This is a useful feature for physically challenged people. You only need to type the characters that make the command unique and device will internally auto complete the command. For example, you could use en instead of enable command. However you cannot use only letter e, since other commands being with letter e like exit.
To utilize abbreviation feature, you need to type the commands and keywords up to the numbers of characters that make it unique abbreviation. For example config t is unique abbreviated form of command configure terminal, so device will accept it and execute the command.
This is an optional features that keep records of EXEC commands that you have entered. This is useful feature specially for recalling complex or long commands such as access list configuration commands. By default history command would keep record of 10 commands, you can change this value from line configuration mode with history size command.
History command will list command in same sequence that you have entered it. Use up arrow key to move in backward sequence and down arrow key to move in forward direction. You can also use show history command from privileged EXEC mode.
Context Sensitive Help command cheat sheet
|(prompt)#?||List all available commands in this mode|
|(prompt)#xx?||List all available commands in this mode that begin with xx ( particular character strings that you have entered)|
|(prompt)#command ?||List all available parameters for command.|
|(prompt)# command keyword ?||List next available argument for command.|
|(prompt)#abbreviated-command [tab key]||Auto complete the partial entered command.|
That’s all for this part in next part I will explain how to take backup of IOS and restore IOS from backup.