(octave.info)Recovering From Errors

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12.1.3 Recovering From Errors
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Octave provides several ways of recovering from errors.  There are
‘try’/‘catch’ blocks, ‘unwind_protect’/‘unwind_protect_cleanup’ blocks,
and finally the ‘onCleanup’ command.

   The ‘onCleanup’ command associates an ordinary Octave variable (the
trigger) with an arbitrary function (the action).  Whenever the Octave
variable ceases to exist—whether due to a function return, an error, or
simply because the variable has been removed with ‘clear’—then the
assigned function is executed.

   The function can do anything necessary for cleanup such as closing
open file handles, printing an error message, or restoring global
variables to their initial values.  The last example is a very
convenient idiom for Octave code.  For example:

     function rand42
       old_state = rand ("state");
       restore_state = onCleanup (@() rand ("state", old_state));
       rand ("state", 42);
       ...
     endfunction  # rand generator state restored by onCleanup

 -- : OBJ = onCleanup (FUNCTION)
     Create a special object that executes a given function upon
     destruction.

     If the object is copied to multiple variables (or cell or struct
     array elements) or returned from a function, FUNCTION will be
     executed after clearing the last copy of the object.  Note that if
     multiple local onCleanup variables are created, the order in which
     they are called is unspecified.  For similar functionality Note:
     The unwind_protect Statement.