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Execute CommandExpressionsInitializationOperation

        @filespec

    Causes SDA to execute SDA commands contained in a file.  Use this command
    to execute a set of frequently used SDA commands.  This command is bound
    to the at sign (@) character.  The name of the file is a required
    argument.

    Some SDA commands allow expressions as command parameters.
    To create expressions, you can use

          Radix operators
          Arithmetic and logical operators
          Precedence operators
          Symbols
          Numerals

    Radix operators specify a given radix for the number that follows the
    operator.  SDA displays hexadecimal numbers with leading zeros and
    displays decimal numbers with leading spaces.

        ^X      Hexadecimal (default)
        ^O      Octal
        ^D      Decimal

    Unary operators

        #       Logical NOT of value
        +       Assigns positive value (default)
        -       Assigns negative value
        @       Uses contents of location
        G       Adds ^X80000000 to value (system space)
        H       Adds ^X7FFE0000 to value (control region)

    Binary operators

        +       Addition
        -       Subtraction
        &       Logical AND
        !       Logical OR
        \       Logical XOR
        *       Multiplication
        /       Division
        @       Arithmetic shift

        Logical AND, logical OR, logical XOR, multiplication, division, and
        arithmetic shifting are performed before addition and subtraction.

    Precedence operators

        Parentheses control the evaluation of all operations.  Expressions
        enclosed in parentheses are evaluated first.  SDA evaluates nested
        parenthetical expressions from the innermost to the outermost pairs
        of parentheses.

    Symbols

        Symbols are composed of up to 31 letters and numbers, and
        can include the dollar sign and underscore characters.  When you
        invoke SDA, it copies the global symbols from SYS.STB, the system's
        symbol table.  You can add other symbols to SDA's symbol table by using
        the DEFINE and READ commands.  SDA also predefines certain symbols,
        some of which follow:

        .       Current location
        G       ^X80000000 (system space)
        H       ^X7FFE0000 (control region)
        R0-R11  General registers
        AP      Argument pointer
        FP      Frame pointer
        SP      Stack pointer
        PC      Program counter
        PSL     Processor status longword

    When you invoke SDA, by using the DCL commands ANALYZE/SYSTEM or
    ANALYZE/CRASH, SDA will execute commands from an initialization
    file if one exists.

    First, SDA searches for the initialization file using the
    logical name SDA$INIT.  If this file is not found, then SDA searches
    for the file SYS$LOGIN:SDA.INIT .

    The initialization file can be used to define keys for SDA commands, or
    automatically execute SDA commands upon invoking SDA.

    You execute the System Dump Analyzer program by means of directives.
    SDA obtains these directives from SYS$INPUT, which can be your terminal
    or a command file.  You can send the output to a file or to your terminal.

    Any of the following commands will invoke SDA:

        $ ANALYZE/CRASH_DUMP dump_file
        $ ANALYZE/SYSTEM
        $ RUN SYS$SYSTEM:SDA

    When a fatal BUGCHECK error causes the system to crash, the system
    writes the current state of the hardware registers and all physical memory
    to a contiguous file called SYSDUMP.DMP in the SYSEXE account on the
    system disk.  Alternatively, the system's paging file may be specified as
    the destination of the dump information instead of SYSDUMP.DMP. This is
    useful on systems that have constrained disk space.

    Note that pages currently in the paging file (paged out) are not saved
    because the paging file is too large.  Although these pages are lost
    from the crash dump, the effect on debugging will be minimal because
    most pages relating to the crash are still in physical memory when
    the crash occurs, and are thus saved in the dump file.  Of course, if the
    paging file is used as a dump file, the pages that are there are wiped
    out.

    It is recommended that the system manager set up the system-startup file
    so that SDA is always run during system startup.  When executed at this
    time, SDA first checks to see if the system has just crashed.  If so,
    SDA executes the SDA commands in the system's startup-command file.
    If the system has not just crashed, SDA exits.

    The following example shows the SDA commands typically included in the
    system's startup file.  The most important of these is the COPY
    command, which copies the dump file to another file.  This operation
    is recommended because the system always overwrites this file in the event
    of a crash, and the record of the previous crash is lost unless another
    copy exists.  Furthermore, if the paging file was used as the dump file,
    the pages that contain the dump information are not available for paging
    until they are explicitly released by the COPY command.

        $ !
        $ !  Invoke the System Dump Analyzer if the system just crashed
        $ !
        $ ANALYZE/CRASH_DUMP SYS$SYSTEM:SYSDUMP
        SET OUTPUT LPA0:SYSDUMP.LIS     ! Make listing file
        SHOW CRASH                      ! Display crash information
        SHOW STACK                      ! Show current operating stack
        SHOW SUMMARY                    ! List all active processes
        SHOW PROCESS/PCB/PHD/REGISTERS  ! Display current process
        SHOW SYMBOLS/ALL                ! Print the system symbol table
        COPY SYS$SYSTEM:SAVEDUMP.DMP    ! Save dump file for later
        EXIT

    If you need more information on the crash, you can execute SDA
    interactively or add SDA commands to the startup file.