COMMAND--Notes

Limits on environment size

If nnnnn is less than 160 or greater than 32768, MS-DOS uses the default
value of 256 bytes and displays the following message:

    Parameter value not in allowed range.

Changing your terminal device

You can specify a different device (such as AUX) for input and output by
using the device parameter. For more information about device, see the
<CTTY> command.

Running multiple command interpreters

When you start a new command interpreter, MS-DOS creates a new command
environment. This new environment is a copy of the parent environment. You
can change the new environment without affecting the old one. The default
size of the new environment is 256 bytes or the size of the current
environment rounded up to the next 16 bytes, whichever is larger. Use the /E
switch to override the default size. (Note that the current environment
refers to the memory actually being used, not to the environment size
specified with the previous /E switch.)

Transient and resident memory

MS-DOS loads the command interpreter in two parts: the resident part (which
is always in memory) and the transient part (at the top of conventional
memory). Some programs write over the transient part of COMMAND.COM when
they run. When this happens, the resident part must locate the COMMAND.COM
file on disk to reload the transient part. The COMSPEC environment variable
identifies where COMMAND.COM is located on the disk. If COMSPEC is set to a
floppy disk drive, MS-DOS might prompt you to insert a disk that contains
COMMAND.COM.

If MS-DOS is loaded in the HMA, a portion of resident COMMAND.COM is also
loaded into the HMA, making more conventional memory available for
programs.

Using the /MSG switch

Usually, MS-DOS leaves many error messages in the COMMAND.COM file on the
disk instead of using memory to store them. When MS-DOS needs to display one
of these messages, MS-DOS retrieves the message from the disk containing
COMMAND.COM.

If you are running MS-DOS from floppy disks instead of from a hard disk,
MS-DOS cannot retrieve such error messages unless you have the disk
containing COMMAND.COM in drive A. If this disk is not present, MS-DOS
displays one of the following short messages instead of the full message:

    Parse error

    Extended error

You can make sure MS-DOS displays complete error messages by using the /MSG
switch with COMMAND. This switch forces MS-DOS to keep these error messages
in memory so that they are always available when needed.

Use the /MSG switch with COMMAND if you have a floppy disk system, unless
you cannot afford to lose the memory used to store the error messages.

You must also specify the /P switch when you use the /MSG switch.

Internal commands

COMMAND is called a command processor because it reads any commands that you
type and processes them.

Some commands are recognized and carried out by COMMAND itself. These
commands are considered internal to COMMAND. Other MS-DOS commands are
separate programs located on your hard disk, which MS-DOS loads just like
your other programs.

  * The following MS-DOS commands are implemented by COMMAND:

    <BREAK>            <ECHO>              <REM>
    <CALL>             <EXIT>              <RENAME (REN)>
    <CHCP>             <FOR>               <RMDIR (RD)>
    <CHDIR (CD)>       <GOTO>              <SET>
    <CLS>              <IF>                <SHIFT>
    <COPY>             <LOADHIGH (LH)>     <TIME>
    <CTTY>             <MKDIR (MD)>        <TYPE>
    <DATE>             <PATH>              <VER>
    <DEL (ERASE)>      <PAUSE>             <VERIFY>
    <DIR>              <PROMPT>            <VOL>