# Tcl catch Command

Most programmers are familiar with the "catch" command to trap and manage errors. 
 However, Tcl's catch command is more than just simple error handling by offering the information you can use to help "debug" your scripts.

## ***catch*** command

The following code snippet demonstrates one of the ways to use a catch command in an if statement.
```
if { [ set returnCode [catch { command args } result returnOptions ]] } {
    # script error found
   } else {
        {
        # no script error
```

After evaluating a script, the *returnCode*, *result*, and *returnOptions* variables contain the return code, result, and a dictionary of return options, respectively. The dictionary will always include a -code and -level entry.

Scripts generating an error yield a return code of 1 (TCL_ERROR) and assign an error message to the *result* variable.  For scripts yielding a return code of 0 (TCL_OK), the *result* variable contains the return value.

Tcl's return and catch commands are inextricably intertwined.  Possible script return include:  0 (TCL_OK), 1 (TCL_ERROR), 2 (TCL_RETURN), 3 (TCL_BREAK), 4 (TCL_CONTINUE).  Note that return codes other than those stated here may also be returned by a given script as the Tcl return command can take several forms:
        return
        return *result*
        return *-code code* *result*
        return *return options value* *result*

For more details on the catch and return commands, visit [tcl.tk catch command](https://www.tcl.tk/man/tcl/TclCmd/catch.html) and [tcl.tk return command](https://www.tcl.tk/man/tcl/TclCmd/return.html) pages respectively.

## Tcl catch command example:  if expression
```
    if { [set returnCode [catch { script args } result returnOptions]] } {
        # Error! - Show contents of variables after catch.
        puts "Error ($returnCode) connecting to broker:  $result"
        # returnOptions includes:  -errorinfo, -errorcode, -errorline, and -errorstack
        dict for { returnOption returnValue } $returnOptions {
            puts "${returnOption}: $returnValue"
       # ... actions required to handle the error ...
        }
    } else {
        # Success! - Show contents of variables after catch.
        # The following statements are for debugging or 
        # information ONLY.  Comment them if not required.
        puts "$returnCode - $result"
        puts for { returnOption returnValue } $returnOptions {
            puts "${returnOption}: $returnValue"
        }
    }
``` 
## Other Error Handling Options:

Other methods to trap and process errors and exceptions include [try / finally](https://www.tcl.tk/man/tcl/TclCmd/try.html).

We could also set a variable to capture the return code of a given command or script and act on it accordingly.

We'll discuss these options in a future post.