catch(n) Tcl Built-In Commands catch(n)______________________________________________________________________________NAMEcatch - Evaluate script and trap exceptional returns
SYNOPSIScatch script ?varName?
_________________________________________________________________DESCRIPTION
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 without raising an error, regardless of any
errors that might occur while executing script.
If script raises an error, catch will return a non-zero integer 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
the variable it names is set to the error message from interpreting
script.
If script does not raise an error, catch will return 0 (TCL_OK) and set
the variable to the value returned from script.
Note that catch catches all exceptions, including those generated by
break and continue as well as errors. The only errors that are not
caught are syntax errors found when the script is compiled. This is
because the catch command only catches errors during runtime. When the
catch statement is compiled, the script is compiled as well and any
syntax errors will generate a Tcl error.
EXAMPLES
The catch command may be used in an if to branch based on the success
of a script.
if { [catch {open $someFile w} fid] } {
puts stderr "Could not open $someFile for writing\n$fid"
exit 1
}
The catch command will not catch compiled syntax errors. The first
time proc foo is called, the body will be compiled and a Tcl error will
be generated.
proc foo {} {
catch {expr {1 +- }}
}
SEE ALSOerror(n), break(n), continue(n)KEYWORDS
catch, error
Tcl 8.0 catch(n)
