Using the catch command

The catch construct is used to prevent errors from aborting a script. The catch construct is a method of isolating errors and allowing you to determine how to proceed. This allows you to present the end user with a customized notification, as opposed to a system-defined error message, which may have no meaning to the user.

In the event an error condition exists, the catch command returns a non-zero integer value corresponding to the Tcl return code. Tcl provides four exceptional return codes. A return value of 1 (TCL_ERROR) indicates that an error has occurred and the value is stored in the result. A return of 2 (TCL_RETURN) is generated by the return command. A return of 3 (TCL_BREAK) is generated by the break command. A return of 4 (TCL_CONTINUE) is returned by the continue command.

If the optionalVarName is provided, it will be set to a dictionary containing the return values. This dictionary (see Chapter 6 for further information on the Tcl Dictionary data type...