Practical Programming in Tcl & Tk, Third Edition

Catch

Until now we have ignored the possibility of errors. In practice, however, a command will raise an error if it is called with the wrong number of arguments, or if it detects some error condition particular to its implementation. An uncaught error aborts execution of a script.^[*] The catch command is used to trap such errors. It takes two arguments:

^[*] More precisely, the Tcl script unwinds and the current Tcl_Eval procedure in the C runtime library returns TCL_ERROR. There are three cases. In interactive use, the Tcl shell prints the error message. In Tk, errors that arise during event handling trigger a call to bgerror, a Tcl procedure you can implement in your application. In your own C code, you should check the result of Tcl_Eval and ...