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]

1  –  Parameter

 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.

2  –  Qualifier

2.1    /PARENT

    Enables you to attach to the parent process. If no parent process
    exists, you receive an error message.

3  –  Description

    The ATTACH command connects your input stream to another process.
    You can use the ATTACH command to change control from one
    subprocess to another subprocess or to the parent process.

    When you enter the ATTACH command, the parent process goes into
    hibernation and your input stream connects to the specified
    destination process. You can use the ATTACH command to connect
    to a subprocess that is part of a current job (left hibernating
    as a result of the SPAWN/WAIT command or another ATTACH command)
    as long as the connection is valid. No connection can be made to
    the current process, to a process that is not part of the current
    job, or to a process that does not exist. If you attempt any of
    these connections, you receive an error message.

    You can also use the ATTACH command in conjunction with the
    SPAWN/WAIT command to return to a parent process without
    terminating the created subprocess. See the description of the
    SPAWN command for more details.

4  –  Example

  $ 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).