OSF DCE Administration Guide--Core Components

Using the DCE Control Program Command Language
Use catch to invoke the rename command as a script.
dcecp> catch {ren move move.old}
1
dcecp>
The catch command treats its argument as a script and executes it, returning a 0 on
successful execution. If an error occurs, it is caught by the catch command which
returns a 1.
You can add a second argument to the catch command. This argument is a variable that
catch modifies to hold the script’s return value (on successful completion) or the error
message. The syntax for the catch command is
catch command varName
One use of catch in scripts is to invoke other procedures. You can read the following
script fragment as follows: ‘‘If the _dcp_create_group procedure returns
unsuccessfully (!= 0) then perform the _dcp_cleanup_user_create procedure and
display the error stored in the msg variable.’’
if {[ catch {_dcp_create_group $group group_created} msg] !=0}{
_dcp_cleanup_user_create $element -principal
error $msg
}
Exceptions are a special class of error generated by the break, continue, and return
commands. You use the break and continue commands to terminate loops such as
while, for, and foreach, and you use the return command to terminate a proc or source
command.
Resulting exceptions can be hard to handle in procedures where loops exist inside (as
part of) a more comprehensive command. For instance, a user-written procedure that
searches for specific object types in CDS might invoke foreach as part of a looping
activity to test for the occurrence of particular attributes.
If you use the break, continue,or return commands to manage loop execution or to
manage some other nested command (like case or if, for example), the parent command
will not be ready to catch the exception. The parent command will abort and issue an
error message as usual. However, the error is associated with the parent command and is
difficult to track to the looping command where it actually occurred.
If it’s necessary to use a continue, break,or return command to terminate a command
that has been called by another command, consider using catch to invoke the nested
command which, in turn, calls the continue, break,or return command to recover from
errors or exceptions. Used this way, the catch command keeps the exception within the
looping or nested procedure where it’s easier to track down.
foreach s [server catalog] {
if {[catch {server show $s} srv_sh_out] != 0} {
continue
}
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