Library /sys$common/syshlp/dbg$help.hlb DEBUG, IF, Example  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  DBG> SET BREAK R DO (IF X .LT. 5 THEN (GO) ELSE (EXAMINE X))

      This command causes the debugger to suspend program execution
      at location R (a breakpoint) and then resume program execution
      if the value of X is less than 5 (Fortran example). If the
      value of X is 5 or more, its value is displayed.