error - Generate an error


error message ?info? ?code?


Returns a TCL_ERROR code, which causes command interpretation to be unwound. Message is a string that is returned to the application to indicate what went wrong.

If the info argument is provided and is non-empty, it is used to initialize the global variable errorInfo. errorInfo is used to accumulate a stack trace of what was in progress when an error occurred; as nested commands unwind, the Tcl interpreter adds information to errorInfo. If the info argument is present, it is used to initialize errorInfo and the first increment of unwind information will not be added by the Tcl interpreter. In other words, the command containing the error command will not appear in errorInfo; in its place will be info. This feature is most useful in conjunction with the catch command: if a caught error cannot be handled successfully, info can be used to return a stack trace reflecting the original point of occurrence of the error:

catch {...} errMsg
set savedInfo $errorInfo
error $errMsg $savedInfo

If the code argument is present, then its value is stored in the errorCode global variable. This variable is intended to hold a machine-readable description of the error in cases where such information is available; see the tclvars manual page for information on the proper format for the variable. If the code argument is not present, then errorCode is automatically reset to ``NONE'' by the Tcl interpreter as part of processing the error generated by the command.


Generate an error if a basic mathematical operation fails:
if {1+2 != 3} {
    error "something is very wrong with addition"


catch, return, tclvars


error, errorCode, errorInfo
Copyright © 1993 The Regents of the University of California.
Copyright © 1994-1996 Sun Microsystems, Inc.
Copyright © 1995-1997 Roger E. Critchlow Jr.