Tcl Shell
TCLSH, short for "Tcl shell," is a shell application for the Tcl programming language. Tcl, which stands for "Tool Command Language," is a scripting language that is supported by most Cisco IOS devices and can be used for various network automation and management tasks.
The Tcl shell in Cisco IOS was designed to execute Tcl commands directly from the Cisco IOS command-line interface. Cisco IOS includes subsystems like Embedded Syslog Manager (ESM) and Interactive Voice Response (IVR), which incorporate Tcl interpreters in their functionality. These subsystems offer unique commands and keyword options that are not available in the standard Tcl shell.
There are various methods to create and execute Tcl scripts within Cisco IOS. Enabling a Tcl shell allows for the input of Tcl commands sequentially. Once entered, these commands are processed by a Tcl interpreter. Recognized Tcl commands are executed, and the outcomes are displayed on the TTY device. Commands not identified as Tcl are passed to the Cisco IOS CLI parser, and if a command is neither Tcl nor Cisco IOS, two error messages are shown. Tcl scripts can also be prepared externally, transferred to the device's flash or disk memory, and executed within Cisco IOS. Additionally, Tcl scripts can be precompiled before being run in Cisco IOS.
The Tcl shell enables the execution of Cisco IOS CLI EXEC commands within Tcl scripts. This functionality allows customers to create guided menus for novice users, automate repetitive operations, and generate customized outputs for show commands.