Provided by: tcl8.4-doc_8.4.20-7_all 
NAME
error - Generate an error
SYNOPSIS
error message ?info? ?code? _________________________________________________________________
DESCRIPTION
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.
EXAMPLE
Generate an error if a basic mathematical operation fails:
if {1+2 != 3} {
error "something is very wrong with addition"
}
SEE ALSO
catch(3tcl), return(3tcl), tclvars(3tcl)
KEYWORDS
error, errorCode, errorInfo