Definitions

A(VM Userid): Indicates the address of the requesting user ID. Unlike some other exits, USERCMND does not have an 80-byte storage area following the user ID.
A(Command): Indicates the address of a 256-byte buffer containing the command exactly as typed by the user except the command has been translated to uppercase. The command is in the first n bytes of the buffer. The variable n is the length passed in the following parameter.
A(Length of command): Indicates the address of a 4-byte field specifying the length of the command entered. The command field always contains the unabbreviated form of the command. CA VM:Tape will truncate any command returned by the exit that exceeds the required length. The command cannot exceed 256 bytes in length.
A(Message buffer): Indicates the address of a 130-byte buffer into which the exit can put a reply message for CA VM:Tape to issue. The message placed in this buffer must be in LINEDIT format, that is, the first byte of the buffer contains the message text length and the message text follows in byte 2 of the buffer.
A(VM account code): Indicates the address of the 8-byte account number obtained from the VMBLOK or ACCTBLOK of the user ID issuing the mount.
A(Common User Exit Buffer): Indicates the address of the 256-byte work area to be used for passing information between the various user exits. This work area is specific to each command being processed by CA VM:Tape and cannot be used across commands.