catch script [ varName ]
The catch command may be used to prevent errors
from aborting command interpretation. Catch calls
the Tcl interpreter recursively to execute script, and
always returns a TCL_OK code, regardless of any errors
that might occur while executing script. The return value
from catch is a decimal string giving the code
returned by the Tcl interpreter after executing
script. This will be 0
(TCL_OK) if there were no errors in script;
otherwise it will have a non-zero value corresponding to one of the
exceptional return codes (see tcl.h for the definitions of code
values). If the varName argument is given, then it gives
the name of a variable; catch will set the variable
to the string returned from script (either a result or an
error message).