Transfers control from your current process (which then
   hibernates) to the specified process in your job.

   The ATTACH and SPAWN commands cannot be used if your terminal has
   an associated mailbox.

   Format

     ATTACH  [process-name]

Additional information available:

ParameterQualifierExample

process-name
   Specifies the name of a parent process or a spawned subprocess to
   which control passes. The process must already exist, be part of
   your current job tree, and share the same input stream as your
   current process. However, the process cannot be your current
   process or a subprocess created with the /NOWAIT qualifier.

   Process names can contain from 1 to 15 alphanumeric characters.
   If a connection to the specified process cannot be made, an error
   message is displayed.

Additional information available:

/PARENT

   Allows you to attach to your process' parent process. If there is
   no parent process, you receive an error message.

   $ SPAWN
   %DCL-S-SPAWNED, process SYSTEM_1 spawned
   %DCL-S-ATTACHED, terminal now attached to process SYSTEM_1
   $ RUN SYS$SYSTEM:SYSMAN
   SYSMAN> ATTACH SYSTEM
   %DCL-S-RETURNED, control returned to process SYSTEM
   $

     In this example, the SPAWN command creates a subprocess
     (SYSTEM_1). After you invoke SYSMAN and enter the ATTACH
     command, you transfer the terminal's control back to the parent
     process (SYSTEM).