Editing Cisco IOS (section)

==Command-line interface==
The IOS [[command-line interface]] (CLI) provides a fixed set of multiple-word [[command (computing)|commands]]. The set available is determined by the "mode" and the privilege level of the current user. "Global configuration mode" provides commands to change the system's configuration, and "interface configuration mode" provides commands to change the configuration of a specific interface. All commands are assigned a ''privilege level'', from 0 to 15, and can only be accessed by users with the necessary privilege. Through the CLI, the commands available to each privilege level can be defined.

Most builds of IOS include a [[Tcl]] interpreter.  Using the [[embedded event manager]] feature, the interpreter can be scripted to react to events within the networking environment, such as interface failure or periodic timers.

Available command modes include:<ref>{{cite web |title=Configuration Fundamentals Configuration Guide, Cisco IOS Release 15M&T |url=https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/fundamentals/configuration/15mt/fundamentals-15-mt-book/cf-cli-basics.html#GUID-A8FDCE6B-9D7D-4213-B6F0-342E394F308E |access-date=14 May 2022 |publisher=Cisco |archive-date=15 May 2022 |archive-url=https://web.archive.org/web/20220515215303/https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/fundamentals/configuration/15mt/fundamentals-15-mt-book/cf-cli-basics.html#GUID-A8FDCE6B-9D7D-4213-B6F0-342E394F308E |url-status=live }}</ref>
* User EXEC Mode
* Privileged EXEC Mode
* Global Configuration Mode
* ROM Monitor Mode
* Setup Mode
And more than 100 configuration modes and submodes.