全面解读DOS 6.0命令集与ANSI.SYS功能详解

DOS命令

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nn Specifies the number of seconds to pause. Acceptable values are from 0 to 99. If 0 is specified, there will

be no pause before defaulting.

Note The first key you assign returns a value of 1, the second a value of 2, the third a value of 3, and so on.

If the user presses a key that is not among the keys you assigned, choice sounds a warning beep (that is, it

sends a BEL, or 07h, character to the console). If choice detects an error condition, it returns an errorlevel

value of 255. If the user presses CTRL+BREAK or CTRL+C, choice returns an errorlevel value of 0.

When you use errorlevel parameters in a batch program, list them in decreasing order.

Examples

What the user sees when you use choice in a batch file

If you use the following syntax in a batch file,

choice /c:ync

the user sees the following when choice is started:

[Y,N,C]?

If you add text to the syntax,

choice /c:ync Yes, No, or Continue

the user sees the following when choice is started:

Yes, No, or Continue [Y,N,C]?

What the user sees if you leave out a prompt

If, as in the following example, you use the /n switch to leave out the prompt in a batch program,

choice /n Yes, No, or Continue?

the user sees only the text you specified when choice is started:

Yes, No, or Continue?

What the user sees if you use the /t switch

If you use the following syntax in a batch program,

choice /c:ync /t:n,5

the user sees the following when choice is started:

[Y,N,C]?

If, after 5 seconds, the user hasn't pressed a key, choice chooses

and returns an errorlevel value of 2. If

the user presses a key before 5 seconds, choice returns the value corresponding to the user's choice.

To have the option of defragmenting drive C when you start your computer, you could add the following lines

to your AUTOEXEC.BAT file:

choice Defrag drive /ty,5

if errorlevel 2 goto SkipDefrag

defrag c:

:SkipDefrag

If you press

within 5 seconds, defrag will not run and choice returns an errorlevel value of 2. If you do

not press

within 5 seconds, or if you choose

, defrag is run on drive C.

Using choice in a batch program

The following batch program demonstrates using the choice option to select one of three programs: MS-DOS

Editor, Microsoft Anti-Virus, or Microsoft Backup.

Notice that the if errorlevel statements are listed in decreasing order. MS-DOS will consider the if statement

true if the errorlevel parameter returned by choice is greater than or equal to the parameter specified in

the if command.

@echo off

cls

echo.

echo A Microsoft Editor

echo B Microsoft Anti-Virus

echo C Microsoft Backup

echo.

choice /c:abc Choose an option

if errorlevel 3 goto MSBackup

if errorlevel 2 goto Msav

if errorlevel 1 goto Edit

:Edit

edit

goto End

:Msav

msav

goto End

:Msbackup

msbackup

goto End

:End

Cls

Clears the screen.

The cleared screen shows only the command prompt and cursor.

Syntax

cls

Command

Starts a new instance of the MS-DOS command interpreter.

A command interpreter is a program that displays the command prompt at which you type commands. Use

the EXIT command to stop the new command interpreter and return control to the old one.

Syntax

command [[drive:]path] [device] [/c string] [/e:nnnnn] [/k filename] [/p [/msg]]

In your CONFIG.SYS file, use the following syntax:

shell=[[dos-drive:]dos-path]command.com [[drive:]path][device] [/e:nnnn] [/p [/msg]]

Parameters

[drive:]path

Specifies where the command interpreter is to look for the COMMAND.COM file when the transient part

of the program needs to be reloaded. This parameter must be included when loading COMMAND.COM for the

first time if the COMMAND.COM file is not located in the root directory. This parameter is used to set the

COMSPEC environment variable.

device

Specifies a different device for command input and output. For more information about this parameter,

see the ctty command.

[dos-drive:]dos-path

Specifies the location of the COMMAND.COM file.

Switches

/c string

Specifies that the command interpreter is to perform the command specified by string and then exit.

/e:nnnnn

Specifies the environment size, where nnnnn is the size in bytes. The value of nnnnn must be in the

range 160 through 32768. MS-DOS rounds this number up to a multiple of 16 bytes. The default value is 256.

/k filename

Runs the specified program or batch file and then displays the MS-DOS command prompt. This switch

is particularly useful for specifying a startup file other than C:\AUTOEXEC.BAT for the MS-DOS Prompt in

Windows. (To do this, open the DOSPRMPT.PIF file using the PIF Editor, and type the /k switch in the

Optional Parameters box.) It is not recommended to use the /k switch on the shell command line in your

CONFIG.SYS file; doing so can cause problems with applications and installation programs that make changes

to your AUTOEXEC.BAT file.

Should be used only when command is used with the shell command in the CONFIG.SYS file. The /p

switch makes the new copy of the command interpreter permanent. In this case, the exit command cannot

be used to stop the command interpreter. If you specify /p, MS-DOS runs your AUTOEXEC.BAT file before

displaying the command prompt. If there is no AUTOEXEC.BAT file in the root directory of the startup drive,

MS-DOS carries out the date and time commands instead. If you do not have a shell command in your

CONFIG.SYS file, COMMAND.COM is automatically loaded from the root directory with the /p switch.

/msg

Specifies that all error messages should be stored in memory. Usually, some messages are stored only

on disk. This switch is useful only if you are running MS-DOS from floppy disks. You must specify the /p

switch when you use the /msg switch. For more information about using the /msg switch, see the Notes

section.

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:

Examples

The following command specifies that the MS-DOS command interpreter is to start a new command

interpreter from the current program, run a batch program named MYBAT.BAT, and then return to the first

command interpreter:

command /c mybat.bat

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

The following CONFIG.SYS command specifies that COMMAND.COM is located in the DOS directory on drive

shell=c:\dos\command.com c:\dos\ /e:1024

This command directs MS-DOS to set the COMSPEC environment variable to C:\DOS\COMMAND.COM. This

command also creates an environment of 1024 bytes for this command interpreter.

Related Command

The shell command is the preferred method of using command to permanently increase space for the

environment table.

Copy

Copies one or more files to the location you specify.

This command can also be used to combine files. When more than one file is copied, MS-DOS displays each

filename as the file is copied.

Syntax

copy [/a|/b] source [/a|/b] [+ source [/a|/b] [+ ...]][destination [/a|/b]] [/v]

Parameters

source

Specifies the location and name of a file or set of files from which you want to copy. Source can

consist of a drive letter and colon, a directory name, a filename, or a combination.

destination

Specifies the location and name of a file or set of files to which you want to copy. Destination can

consist of a drive letter and colon, a directory name, a filename, or a combination.

Switches

Indicates an ASCII text file. When the /a switch precedes the list of filenames on the command line, it

applies to all files whose names follow the /a switch, until copy encounters a /b switch, in which case the /b

switch applies to the file whose name precedes the /b switch.

When the /a switch follows a filename, it applies to the file whose name precedes the /a switch and

to all files whose names follow the /a switch, until copy encounters a /b switch, in which case the /b switch

applies to the file whose name precedes the /b switch.

An ASCII text file can use an end-of-file character (

CTRL+Z

) to indicate the end of the file. When

combining files, copy treats files as ASCII text files by default.

Indicates a binary file. When the /b switch precedes the list of filenames on the command line, it

applies to all files whose names follow the /b switch, until copy encounters an /a switch, in which case

the /a switch applies to the file whose name precedes the /a switch.

When the /b switch follows a filename, it applies to the file whose name precedes the /b switch and

to all files whose names follow the /b switch, until copy encounters an /a switch, in which case the /a

switch applies to the file whose name precedes the /a switch.

The /b switch specifies that the command interpreter is to read the number of bytes specified by the

file size in the directory. The /b switch is the default value for copy unless copy is combining files.

Verifies that new files are written correctly.

Notes

Copying to and from devices

You can substitute a device name for one or more occurrences of source or for destination.

Using or omitting the /b switch when copying to a device

When destination is a device (for example, COM1 or LPT1), the /b switch causes MS-DOS to copy data to the

device in binary mode. In binary mode, all characters (including such special characters as

CTRL+C

CTRL+S

CTRL+Z

, and carriage return) are copied to the device as data. Whereas, omission of the /b switch causes

MS-DOS to copy data to the device in ASCII mode. In ASCII mode, such special characters as those

previously listed may cause MS-DOS to take special action during the copying process.

Using the default destination file

If you do not specify a destination file, MS-DOS creates a copy with the same name, creation date, and

creation time as the original file, placing the new copy in the current directory on the current drive. If the

source file is on the current drive and in the current directory and you do not specify a different drive or

directory for the destination file, the copy command stops and MS-DOS displays the following error message:

File cannot be copied onto itself

0 File(s) copied

Using the /v switch

If MS-DOS cannot verify a write operation, it displays an error message. Although recording errors rarely

occur with the copy command, the /v switch lets you verify that critical data has been correctly recorded.

The /v switch also slows down the copy command, because MS-DOS must check each sector recorded on

the disk.

Using the /a and /b switches

The effect of an /a or /b switch depends upon its position on the command line. When the /a or /b switch

follows the source filename, copy performs as shown in the following list:

Treats the file as an ASCII (text) file and copies data that precedes the first end-of-file character.

Copy does not copy the first end-of-file character or the remainder of the file.

Copies the entire file, including any end-of-file character.

When the /a or /b switch follows the destination filename, copy performs as shown in the following

list:

Adds an end-of-file character as the last character of the file.

Does not add an end-of-file character.

Combining files with the copy command

If you specify more than one source, separating entries with a plus sign (+), copy combines the files,

creating a single file. If you use wildcards in source but specify a single filename in destination, copy

combines all files matching the filename in source and creates a single file with the filename specified in

destination.

In either case, copy assumes the combined files are ASCII files unless you specify the /b switch. (Do not

combine non-ASCII files without specifying the /b switch; doing so can result in truncated files, since most

binary files contain

CTRL+Z

characters which cause copy to behave as if it has reached the end of the file.)

If the name of the destination file is the same as the name of one of the files being copied (except the first

file), the original contents of the destination file are lost. When this happens, copy displays the following

message:

Content of destination lost before copy

Copying files in subdirectories

To copy all of a directory's files and subdirectories, you should use the xcopy command.

Copying zero-length files

Copy does not copy files that are 0 bytes long. Use xcopy to copy these files.

Changing the time and date of a file

If you want to assign the current time and date to a file without modifying the file, use a command in the

following format. The commas indicate the omission of the destination parameter.

copy /b source+,,

Examples

The following command copies a file and ensures that an end-of-file character is at the end of the copied file:

copy memo.doc letter.doc /a

To copy a file named ROBIN.TYP from the current drive and directory to an existing directory named BIRDS

that is located on drive C, type the following command:

copy robin.typ c:\birds

If the BIRDS directory doesn't exist, MS-DOS copies the file ROBIN.TYP into a file named BIRDS that is

located in the root directory on the disk in drive C.

To copy several files into one file, list any number of files as source parameters on the copy command line.

Separate filenames with a plus sign (+) and specify a filename for the resulting combined file, as the

following example shows:

copy mar89.rpt + apr89.rpt + may89.rpt report

This command combines the files named MAR89.RPT, APR89.RPT, and MAY89.RPT from the current drive and

directory and places them in a file named REPORT in the current directory on the current drive. When files

are combined, the destination file is created with the current date and time. If you omit destination, MS-DOS

combines the files and stores them under the name of the first specified file. For example, if a file named

REPORT already exists, you can use the following command to combine all four files in REPORT:

copy report + mar89.rpt + apr89.rpt + may89.rpt

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