Introduction to DOS

University of Strathclyde Computer Centre
Curran Building
100 Cathedral Street
Glasgow

These course notes are intended to be used as an introduction to MS-DOS version 5.0 although much of the material is also relevant to version 6 and its revisions.

They are not intended to be a sole source of reference for anyone learning or using DOS; reference will need to be made to the on-line Help utility and/or appropriate manuals as necessary.

After a number of introductory pages and background material the rest of the course is largely 'hands-on'.

DOS is an operating system used on PCs (Personal Computers).

The Operating System is software which controls the hardware of the machine (the disks, keyboard, mouse, monitor, etc.) and allows the user's programs and packages to be run on the machine. It is the interface between your word processor or spreadsheet or other program and the electrical signals which the CPU (the Central Processing Unit or Processor), the heart of the computer, understands.

Sometimes DOS is stored on a Diskette, but normally it is stored on the Hard Disk, and it is easier to use when it is.

As with all programs (or software), different parts of DOS are brought into RAM and executed as they are needed.

To actually perform or execute the instructions that make up computer programs they have to be brought into the Main Memory or RAM (Random Access Memory) of the computer. This an electronic medium and so when the machine is switched off and the power is lost the contents of memory are lost. Hence RAM is often characterised as Temporary Storage.

In order to preserve the instructions in a computer program (as well as computer data in general) a Permanent Storage medium is needed. This is provided by Disks and Tapes (Magnetic Media). Programs and data stored on disk or tape are not lost when the computer is switched off.

Once the computer has been switched on or 'powered up', programs and data are moved from permanent storage (usually the Hard or Fixed disk inside the computer but possibly a floppy disk or a tape) to Main Memory / RAM as required. When they need to be saved permanently they are written from Memory / RAM back to disk (or tape).

The capacity of any computer storage medium is usually measured in Bytes, Kilobytes or Megabytes.

A Byte can store 1 character.
1 Kilobyte (KB) is equivalent to 1,024 bytes and so stores 1,024 characters.
1 Megabyte (MB) is equivalent to c.1,000,000 (1,024 x 1,024) bytes/characters.

How do Disks and Tapes compare -

Cost - based on the same storage capacity, a Tape/Cassette is much cheaper than a Hard Disk. e.g. 520 MB storage - tape c. £12-13, Disk c. £170.
Speed of Accessing (Retrieving) stored information - a Disk is much faster than a Tape.

Therefore, because of its speed compared to tape, disk is the permanent storage medium which forms part of the computer system; whereas because of its cheapness and portability tape may be used for large scale backup/archiving (e.g. Hard Disk backup).

How does RAM compare -

Speed - much faster than disk (or tape).

Cost - more expensive than disk or tape (e.g. £25 - £30 for 1MB).

Storage Capacity - less than hard disk or tape.

More about Disks -

The Disk Operating System (DOS) is a computer program which is loaded from disk into the main memory of an IBM compatible PC, when the machine starts up, to control its operations. 'IBM compatible PC' is a generic term used to refer to the majority of PCs, made by a number of manufacturers, e.g., Viglen, DEC, Compaq, Dell, IBM etc., which all run DOS. This term has come to mean, in effect, all PCs other than Apple Macintosh personal computers, (commonly referred to as Macs, rather than PCs) and Mac clones.

Over recent years three companies have produced DOS (or a brand of it); Microsoft, IBM and Novell. The latter has now dropped out of the market and IBM's share is marginal. Microsoft DOS i.e. MS-DOS is now the de facto standard.

Here is a summary of the development of Microsoft DOS (MS-DOS)

Version Year Features
1.0     1981 Original Disk Operating System
1.1     1982 Support for double-sided disks
2.0     1983 Support for sub directories
2.01    1983 Support for international symbols
2.25    1983 Bug fixes
3.0     1984 Extended character set, large hard disks
3.1     1984 Support for PC networks, bug fixes
3.2     1986 Support for 3.5-inch disks
3.3     1987 Support for PS/2 computers
4.0     1988 Support for large partitions
4.01    1989 Bug fixes
5.0     1990 New shell, new editor, smaller kernel, memory management
6.0     1993 Disk Compression, better Memory Management, and 
        AntiVirus software now included in the operating software.
        had to be bought separately, as Utilities. 6.0 Contained
        a number of bugs.
6.2     1993 Microsoft claims it was not a bug fix for 6.0, but most
        observers saw it as that.

DOS is composed of a number of files. You can choose to keep all of its components available on disk so that you can use all the facilities it offers (this is the norm if space is not a constraint). Alternatively you may choose to have a minimal setup in which case not all of its features will be available. However at a minimum there are three system files which you must have.

These are IO.SYS, MSDOS.SYS and COMMAND.COM.

The disk which your computer uses to load and run DOS must contain these files and is called the System, or Startup, or Boot, disk.

COMMAND.COM, the command processor (or shell) is the part of DOS that executes (or processes) the commands we will be looking at. These commands are either internal to the command processor (i.e. part of it), or external to it.

You must not create a file with the same name as an Internal Command. Examples of such commands are DIR, DEL and COPY, which are part of the COMMAND.COM program. You will find that the names of these commands cannot be seen when you list the files on your disk.

All IBM compatible PCs have a program which is not part of DOS but interacts with it to provide peripheral device support. This software is called the BIOS (Basic Input/Output System) and it contains the basic instructions for controlling such things as the disk drives (see below), keyboard and serial/parallel ports while the machine is running. It also contains instructions for testing various parts of the computer (e.g. memory, floppy disk drives and the various interfaces) which are executed when the computer is starting or 'powering' up. This POST (Power On Self-Test) routine will display a message if there are any problems.

Disk drives are those parts of the computer hardware which hold the disks and perform the writing and reading of data to and from disk. Within a DOS command line they are referenced by a letter plus a colon. The hard disk drive, containing the large capacity, fast access, fixed disk, is normally referred to as C:(i.e. the C drive), the floppy drive is A: and if there is a second floppy drive it is B:

When your PC is running a Prompt appears at the left of the screen indicating that the computer is ready for you to type in commands. This System, or DOS, or Command, Prompt includes a letter to indicate the current or default drive. That is the disk drive DOS will use when executing the command if no other is specified in the command line. For example A>and C> are both common prompts indicating the floppy and hard drives respectively.

When the floppy disk drive writes data to a floppy disk it places it in concentric circles called tracks. A floppy disk contains either 40 or 80 tracks each of which is divided into small sections called sectors, each sector containing 512 bytes. The disk drive contains a read/write head which moves from one track to the next as the disk rotates either finding data to be read, or locating free space to which it can write (depending on whether DOS has requested a read or write operation).

The following table shows the types of disk drives (for floppy disks / diskettes) a personal computer can have

5.25 " Single-sided Double-Density 160KB/180KB 40 Tracks 8/9 Sectors
5.25 " Double-sided Double-Density 320KB/360KB 40 Tracks 8/9 Sectors
5.25 " Double-sided High-Density 1.2MB 80 Tracks 15 Sectors
3.5 " Double-sided Double-Density 720KB 80 Tracks 9 Sectors *
3.5 " Double-sided High-Density 1.44MB 80 Tracks 18 Sectors *
3.5 " Double-sided High-Capacity 2.88MB 80 Tracks 36 Sectors

* indicates the 2 most common types of floppy.

On a floppy disk it is possible to physically enable or disable writing to the disk. This allows you to prevent accidental writing to the disk or unintentional formatting of the disk.

To disable writing to a 5.25" floppy disk a notch called the write protect notch should be covered by non transparent tape on both side of the disk.

Always ensure that you insert your diskette in the correct way, namely - the label side should be up, and the edge containing the silver slider should go into the machine first.

Formatting a disk creates the following data structures on it -

The Root Directory - This contains the name, attributes (see later), time and date of last modification and size of each file on the disk. It also identifies the disk location of the first cluster of each file.

A Cluster, or Allocation Unit, is a group of consecutive sectors (in the case of a floppy disk 2 sectors). It is the smallest unit of disk space that can be allocated to a file.

Files are divided into clusters because there is not always a single piece of free disk space big enough to accommodate a particular file. Therefore it has to be broken up and distributed over different parts of the disk where there is free space i.e. where there are free clusters. As a result of this files, and disks themselves, are often referred to as being fragmented, a characteristic which slows down the processes of writing to and reading from the disk.

The File Allocation Table (FAT 1) - After the first cluster of a file has been located the FAT is used to locate subsequent clusters. It contains the address of each subsequent cluster in the allocation chain.

FAT 2 - A copy of FAT 1 which DOS uses to verify the integrity of the filing system.

It is possible to store hundreds of files on a disk and it can a tedious task trying to find a particular one you are looking for if they are not categorised in any way. Therefore DOS allows you to group related files together in directories. The main directory on a disk is called the ROOT directory, which is represented by \ (a back slash) and it is created by DOS when formatting the disk. You can create directories in the ROOT directory and within each other and they can each contain a number of files. The directory structure is often thought of as an inverted tree structure with the root at the top branching down into lower layer directories and subdirectories. For example -

Data and programs are stored on disks in files. DOS itself consists of a number of files working together to provide the operating system. Other computer programs such as word processors and spreadsheets are also constructed from a number of files. When you save work produced with one of these packages (e.g. a document from a word processor) you save it to a file. When naming a file it is always a good idea to use a name which indicates the contents of the file. Likewise when naming a directory, which is a special type of file, you should use a name which helps to identify the files it contains.

DOS has certain rules governing the naming of files -

Filenames are not case sensitive.
Maximum length allowed for a filename is 8 characters.
Maximum length allowed for the extension to a file name is 3 characters.
The file name and extension are separated by a . (period).
Characters not permitted in naming files are
. " / \ [ ] : | < > + = ; , ? ^ * And Spaces
These characters have special meaning when used in or with a file name.

File extensions can have special meaning to DOS or other programs and are often used to indicate the type of a file.

e.g. The .BAT extensions signifies a Batch files. A batch file contains a batch or group of DOS commands which are performed one after the other when the file is executed (or run). You execute a batch file by typing its name, without the .BAT extension, at the DOS prompt. AUTOEXEC.BAT is a batch file which is often found on the boot disk. DOS accesses this file in the last stage of booting (i.e. starting) your system and executes each command it contains.

Here are some commonly used extensions and the type of file they indicate

BAK Backup file
BAS Basic program
BAT Batch file; it contains a group of DOS commands the user wants to run
COM Command file
DOC Document
EXE Executable file, Similar to COM file
PRN Print file
SYS System file
$$$ Temporary file

These follow the same rules as ordinary file names except that extensions are not allowed in version 5 and earlier versions of MS-DOS. Remember that a directory is just a special kind of file - i.e. a file which can contain other files.

Commands are entered at the DOS prompt, e.g. A> or C> or F> which, as previously noted, informs you of the default or current drive. The exact form of the initial prompt depends on what type of disk booted the computer and whether the startup file AUTOEXEC.BAT, has customised the prompt. A letter plus > (greater than sign) is the default prompt.

For example A> indicates that the computer was booted with a floppy disk, whereas C> means the computer was booted from a hard disk and F> indicates that the computer may have been booted from a networked machine.

A command line can contain just a command itself i.e. a single word, but most commands can take parameters (or arguments) indicating files or directories on which the command is to operate. Parameters are separated from commands by one or more spaces.

You finish a command line by typing the Return or Enter key (<return> or <enter), and this signals the computer that you have finished typing in your command and that it should carry it out.

An example of an acceptable DOS command is

CLS

Unless you specify in a command line a particular (Disk) Drive to use, DOS will attempt to

execute the command on the current, or default, drive. i.e. It will look for the directories and files referenced in the command line on the disk in the drive indicated by the screen prompt, e.g.

A> (diskette)

C> (hard disk)

Suppose the current/default drive is C and you are going to perform a lot of operations on your diskette in drive A. To avoid typing A: in your command line every time you execute a command you can change the default drive.

To change the default drive from C to A type A: <return>

The prompt will now include A instead of C

To make C the default drive again type C: <return>

Very usefully DOS buffers (i.e. remembers) the last command you typed in. If you want to run that command again simply press F3 and then <return> to run it. Alternatively you can press the F1 or key repeatedly until your command reappears, and then <return>.

F3 Recalls the last command the user entered

F1 or Recalls the last command the user entered a character at a time

 command-name DRIVE:\PATH\DIRECTORY /SWITCHES
                        FILE

This is a simplified illustration of the basic format of DOS command lines. The command-name is of course essential but, depending on what that command is, the other elements of the command line may or may not be present. Moreover some command lines will contain additional elements not included in this example. The components of the command line are explained below.

(Note - it is not necessary to understand this abstract illustration of the DOS command line as examples are given for each of the commands discussed in these notes. Indeed you might prefer simply to look at the actual commands.)

The components of the command line are -

command-name = a DOS command

DRIVE: = a letter plus colon indicating the relevant disk (drive) for the following path and directory/file.

Usually
C: for the hard disk drive.
A: for the floppy disk drive.
B: if there is a second floppy disk drive.
F: for a network disk.

PATH = a hierarchy of directories, each preceded by a \ (back slash), from the Root directory of the disk (represented by the first \) to the directory containing the directory or file on which the command is to be executed.

e.g. \faculty\dep_ment\admin

Note - If you are already in the directory which contains the file or directory to be manipulated then the drive and path do not need to be specified.

DIRECTORY = the directory on which the command is to be executed.

or FILE = the file on which the command is to be executed.

If a path has been specified then a \ must be placed before this item to separate it from the path.

e.g. \faculty\dep_ment\admin\minutes.doc

SWITCHES = ways of modifying the operation of the command.

Throughout the notes, a number of possible switches are listed for each

command, however often no switches will be required.

Switches can usually be combined - i.e. you can have more than one switch for a particular command.

Note - Very often elements of this syntax can be omitted, in which case DOS will use defaults. e.g. If no DRIVE: is specified in the command line, then DOS attempts to execute the command on the current drive (i.e. that indicated by the screen prompt). If no PATH is specified, then DOS attempts to execute the command in the current directory (i.e. the directory in which you are currently working).

An example of how the commands are presented in the notes is now given using the DIR command. The command name and a brief note of what it does is given in the heading, followed by a little more explanation, its syntax and some examples.

DIR - Lists files and subdirectories

This command lists information about files and subdirectories and the amount of free disk space.

Command Syntax: DIR DRIVE:\PATH\DIRECTORY /SWITCHES
                              FILE

Where SWITCHES are

P - page through the screens

W - produce a wide listing

Example: List the contents of the root directory of the hard disk

If what you type on the command line is not a valid DOS command, e.g. if you type in rubbish, or misspell a command, you will probably get the following response.

Bad command or file name

Likewise if you type in the name of a command correctly but add too many parameters, or an invalid switch to it, DOS will respond with an appropriate error message.

Version 5 of DOS came with a command which helps the user establish what each DOS command can do. (DOS 6 provides a similar, more graphical facility.)

Command Syntax: HELP command-name

Example 1: Display a brief description of what all the DOS commands do.

HELP

Example 2: Display more information about a particular command e.g. DIR

HELP DIR

or DIR / ?

Disk Manipulation

• FORMAT - formats a disk
• SYS - makes a disk a System disk
• UNFORMAT - unformats a disk
• DISKCOPY - makes a copy of a diskette

A disk must be formatted for a particular operating system before it can be read from or written to by that operating system. DOS formatting creates a new root directory and file allocation table on the disk, it also destroys anything already on the disk. Therefore do not format a disk until you are sure there is nothing on the disk that you want to preserve.

You will not normally need to format a disk a second time (i.e. after your initial format of a blank disk). If you do reformat a disk, all existing data on it will be destroyed.

Command Syntax: FORMAT DRIVE /SWITCHES

Where SWITCHES are

S - create a DOS system/boot disk - i.e. Format the disk and automatically install the DOS system files (IO.SYS, MSDOS.SYS and COMMAND.COM) on it

F:x - where x is the floppy disk size i.e. one of 160, 180, 320, 360, 720, 1.2, 1.44, 2.88

The F switch is most commonly needed if formatting a DD (Double Density) disk in a HD (High Density) drive. Specifically, formatting a 3.5" 720 KB disk in a 3.5" 1.44 MB drive, e.g.

FORMAT A: /F:720

If you use the FORMAT command without switches on a 3.5" disk in a HD (1.44 MB) drive, DOS will attempt to format that disk to 1.44 MB even if it is a DD disk. This will result in a disk which is unreadable on DD drive machines. By using the F:720 switch the disk will be readable on both types of machine.

Other SWITCHES

T:t - where t is the number of tracks per disk side
N:s - where s is the number of sectors per track

Together these provide an alternative to the F:x switch for specifying the size of the disk being formatted, e.g.

FORMAT A: /T:80 /N:9

can be used to perform the same format as using F:720 above.

Remember -
a machine with a HD drive can read and format both HD and DD disks.
a machine with a DD drive can read and format only DD disks.

Examples using the FORMAT command -

Example 1: Format a HD floppy disk in a HD drive

FORMAT A:

Example 2: Format a disk as a DOS System disk

FORMAT A: /S

Example 3: Format a 3.5" DD 720 KB disk in a 3.5" HD 1.44 MB drive

FORMAT A: /F:720

If you already have a formatted disk which you want to be able to use as a System (or Boot) disk, you can install the 3 essential system files to it using this command.

Example: Make the diskette in drive A a system disk by installing the system files on the hard disk to it

SYS C: A:

The UNFORMAT command is a limited safe guard introduced in DOS 5 to recover data from a disk which have been lost as a result of performing a FORMAT.

You should not really need to use this command if you are careful. It is good practice always to use the DIR command on a disk to see if it has already been used before trying to format it. If DIR displays information about files and directories or disk space then the disk is already DOS formatted. (However this simple test does not let you know if the disk has already been formatted but for a Macintosh computer.)

Note - Unformatting a disk only works if the UNFORMAT command is used before putting any new files on it.

Command Syntax: UNFORMAT DRIVE: /SWITCH

Where SWITCH is

TEST - display only, non committal of data. This shows how UNFORMAT would attempt to recreate the information on the disk, but does not actually unformat the disk and do so.

Example 1: Test to see how a disk would be recovered from a format

UNFORMAT A: /TEST

Example 2: Actually recover from use of the FORMAT command

UNFORMAT A:

DISKCOPY makes an exact copy of one floppy disk (the source disk) on another (the destination or target disk). The original contents of the destination disk are destroyed. If the destination disk is unformatted DISKCOPY will format it. The disks should be of the same type (e.g. two 1.44 MB HD disks), however if the destination disk is of a different type from the source disk DISKCOPY will try to format it to match the source diskette but this may not be possible.

Note - The XCOPY command (see later) is the best command to use when copying files between different types of disk (e.g. a 720 KB DD disk and a 1.44 MB HD disk), or when you want to preserves the original contents of the destination disk.

Command Syntax: DISKCOPY DRIVE1:         DRIVE2:
                         (source disk) (destination disk)

Example 1: Make a copy of a diskette using two identical drives. (The copy will be from the diskette in drive A to the diskette in drive B)

DISKCOPY A: B:

If you only have one floppy disk drive, which is normal, you can still make an exact copy of a diskette. You specify drive A twice in the command line, start the copy with the source diskette in that drive, and swap it with the target diskette as directed during the copying operation until the copy is complete.

Example 2: Make a copy of a diskette using one drive

DISKCOPY A: A:

• MD or MKDIR - creates a directory
• CD or CHDIR - changes directory
• PROMPT - changes the command prompt
• TREE - displays the directory structure
• RD or RMDIR - removes a directory
• Renaming directories PATH - creates a search path

The MD or MKDIR command is used to create subdirectories in the root directory or other subdirectories.

Command Syntax: MD DRIVE:\PATH\DIRECTORY

Example 1: Create a subdirectory named DOCS in the root directory of C

MD C:\DOCS

Example 2: Create a subdirectory of the DOCS subdirectory called WORK

MD C:\DOCS\WORK

Example 3: Create a subdirectory of WORK called TEMP

MD C:\DOCS\WORK\TEMP

Example 4: If you were already in the WORK directory (see next section re changing directory) the following would be sufficient to create the TEMP subdirectory

The CD or CHDIR command is used to move from one directory to another; or to show the current directory path (i.e. the hierarchy of directories from the root directory to the one you are currently working in). The directory you are currently in is known as the current or default directory. When you move to another directory it becomes the current directory. Once your system has booted your initial current directory will normally be the root.

Command Syntax: CD DRIVE:\PATH
             or CD

DOS uses the following 'special' characters to reference particular directories within the directory structure and these can also be used with the CD command.

\ - the Root Directory
. - the Current Directory
.. - the Parent Directory of the current directory

Example 1: Move to the subdirectory TEMP (assuming it exists)

CD C:\DOCS\WORK\TEMP

Example 2: Display the path to the current directory (i.e. Current Directory Path)

CD

Example 3: Move to the parent directory of the currentdirectory

CD ..

Example 4: Move back to the subdirectory TEMP (this example assumes you are currently in subdirectory WORK; use example 2 to check before moving)

CD TEMP

Example 5: Move to the root directory. (This will make the root the current directory)

It is useful if you can see immediately from the command/screen prompt what directory you are currently working in (i.e. the current directory) and the path to that directory. The PROMPT command enables you to do this.

To make the command prompt show the path to the current directory, and not just the letter representing the default disk drive, type

PROMPT $P$G

Your AUTOEXEC.BAT file may already include this command line, if not it can be edited to do so. In this way a useful prompt will be set up every time you start a new session on your computer.

The TREE command enables the user to obtain a graphical view of the structure of directories and subdirectories on a disk.

Command Syntax: TREE DRIVE:\PATH /SWITCH

Where SWITCH is

F - Display the names of files in each directory

Example 1: Display the structure of the DOCS directory

TREE C:\DOCS

Example 2: Display the directory structure and files of C

RMDIR or RD is used to remove a directory. This command will only work if the directory concerned is empty.

Command Syntax: RD DRIVE:\PATH\DIRECTORY

Example: Remove the empty subdirectory of C:\DOCS\WORK called TEMP

RD C:\DOCS\WORK\TEMP

For many DOS commands (viz. external commands) there is a program file which has to be executed in order for the command to work. In the examples so far we have assumed that this is not a problem but in fact DOS has to know where on disk, i.e. in which directory, the corresponding program file is. If it cannot find the file then the command will fail.

By default DOS will only look in the current directory for this program/executable file. If it is not there then DOS has to be know the path (i.e. the hierarchy of directories from the root) to it.

This can be achieved by prepending the relevant path to the command name whenever composing a command line. However it would be better if DOS could simply be told in which directories to look for program files whenever a command name was entered. This can be achieved by using the PATH command. It enables you to specify the path to directories DOS should search, after the current directory for the program file for a command. Once this command has been issued DOS will remember these directories until the command is used again either to clear the search path or set a new search path, or until the machine is switched off.

Command Syntax: PATH DRIVE:\PATH

You can have multiple occurrences of DRIVE:\PATH each separated by ;

Example 1: Set a path to \ (the root directory), and the DOS directory

PATH C:\;C:\DOS

This instructs DOS that after it has searched the current directory for a program file, it should then search the root directory of C: and then the DOS subdirectory of the root.

This should be a minimum search path when using DOS because most of the DOS program files are usually kept in the DOS subdirectory and the root directory. It allows the DOS commands to be used, as in these notes, without prepending them with a path.

A search path containing at least these elements is usually set up in the AUTOEXEC.BAT.

Example 2: Add the directory MEMOS on the diskette to the search path

PATH C:\;C:\DOS;A:\MEMOS

You can also use the PATH command to see what directories are currently in the search path, and to clear it.

Example 3: Display the current search path

PATH

Example 4: Clear the search path

PATH ;

• DIR - Lists files and subdirectories
• Wildcard Characters ? *
• EDIT - creates a new file or modifies an existing file
• COPY - copies a file or a group of files
• XCOPY - copies all files in a directory (and its subdirectories)
• DEL or ERASE - deletes a file or a group of files
• UNDELETE - undeletes files
• COPY (or XCOPY) plus DEL - moves files
• DOSKEY - recalls commands
• RENAME or REN - renames files
• TYPE - displays text files
• PRINT - prints a text file
• COPY - used to create a file
• ATTRIB - sets file properties
• FC - compares two files

This command lists the names of files and directories in the current directory, or one specified in the command line. It can also provide additional information such as the amount of free space on the disk, the dates directories were created, and the dates files were last modified and there sizes.

It is also possible use DIR to search for specific files.

Command Syntax: DIR DRIVE:\PATH\DIRECTORY /SWITCHES
                               FILE

Where SWITCHES are

P - page through the listing one screen at a time
W - produce a wide listing
S - execute the command in subdirectories of the
subject directory as well as the directory itself
A:x - list only files with attribute x where x = h (hidden), r (read only), s (system)
O:y - order the listing according to y where y = n (name), e (extension), s (size), d (date and time - earliest first)
B - blank out heading and summary information

Example 1: List the contents of the root directory of the floppy disk

DIR A:\

Example 2: Produce a wide listing of the current directory of C one page at a time

DIR C: /P /W

Example 3: List every occurrence of the file AUTOEXEC.BAT in the current directory and its subdirectories

DIR AUTOEXEC.BAT /S

Example 4: List the contents of the DOS directory in chronological order

DIR C:\DOS /O:D

Example 5: List only those files in the root of C which are hidden

A Wildcard Character is a character which has special meaning. In DOS wildcards are the * (the asterisk) and ? (the question mark ). They are usable with many DOS commands. The question mark represents any single character, and the asterisk a string of characters. Wildcards enable you to do more with the basic commands.

As examples, suppose you wanted to use the DIR command to list only the files that ended with a particular extension, or started with a particular word.

Example 1: Display only those files in the root of C whose name ends with the .COM extension

DIR C:\ *.COM

Example 2: Display those files in the DOS directory which start with DISK, are followed by 4 characters, and have any extension.

DIR C:\DOS\DISK????.*

To create a text file in DOS you invoke the Screen Editorby using the EDIT command.

Command Syntax: EDIT DRIVE:\PATH\ FILE

FILE must be an unformatted ASCII text file

Carry out the following steps to create your own file; this will give you a file on which to practice the other commands.

Type EDIT <return> at the DOS prompt.
Once in the editor press the ESC key.

You should get the following screen

Then type in the bold text below, using your own name where it says your name. This text will constitute the contents of the file.

(If you make a mistake while typing use the following keys to make corrections. - The Delete and BackSpace keys to remove letters; the (Arrow) keys to position the Cursor without removing letters; and the Insert key to switch between Insert and Over Write mode.)

@echo off
echo.
echo GOOD DAY your name
echo.

Once you have finished press the Alt key which, as indicated at the bottom of the screen, activates the menus.

You will see the first letters of the Menu Items at the top of the screen become illuminated. The File item should be highlighted. If not use and to highlight it. Press the Return or Enter key to activate the File Menu. Use to move the menu Bar down to Save As, and press <return< to select this option.

Type in the file name HELLO.BAT <return>. You have now created a file called HELLO.BAT, containing the above text. Now leave the Editor by activating the File Menu, and then selecting Exit.

The file you have just created is a simple Batch file - i.e. a file of DOS commands which will be executed, one after the other, simply by typing in the name of the file (withoutthe .BAT extension).

To run this batch file type HELLO <return> at the DOS prompt.

The message Good Day should appear.

The Editor provides an easy method of creating a new text file. It is particularly useful for creating DOS batch files (which are special text files). If you want to modify/edit an existing text file then you simply supply the name of that file as a parameter to the command. Once in EDIT you can use a mouse, or simply the keyboard, to highlight text, cut (or copy) and paste that text, select menu items, etc. Most of the commands in EDIT are self explanatory and easy to use.

Example: Edit the batch file you have just created.

EDIT HELLO.BAT

The COPY command enables you to make copies of files. It may be used to make a copy within a particular directory, to copy from one directory to another and to copy from one disk to another. You can use the command to copy one file by using its filename, or several files by using the DOS wildcard characters * and/or ?

Command Syntax: COPY DRIVE1:\PATH1\ FILE1(S) DRIVE2:\PATH2\ FILE2(S)

Example 1: Copy one file from drive C to drive A

COPY C:\HELLO.BAT A:

Example 2: Make a copy of a file within the same directory. You have to give the copy a different name. e.g. GREETING.BAT

COPY A:\HELLO.BAT A:\GREETING.BAT

Example 3: Copy all the files in the root of A to a directory on the hard drive

COPY A:\*.* C:\DOCS

Now use the DIR command to list the files on drive A again.

The XCOPY command behaves in the same way as the COPY command, however it allows the copying of all the files in a directory, and also its subdirectories.

Command Syntax:

XCOPY DRIVE1:\PATH1\DIRECTORY DRIVE2:\PATH2 /SWITCHES
                   FILES

Where SWITCHES are

S - copy subdirectories which contain files
E - also copy empty subdirectories (/E is used with /S)
D:date - only copy files changed after a certain date

Example 1: Copy the contents of the DOCS directory, and its subdirectories, including empty ones, to directory TEMP-DIR on A

XCOPY C:\DOCS A:\TEMP-DIR /S /E

DOS will allow you to create the TEMP-DIR if it does not already exist.

Example 2: Copy all the files in the root directory of C modified on or after 1/1/96 to A

XCOPY C:\*.* A: /D:1/1/96

Example 3: Copy all the files in the A drive's TEMP-DIR directory to a directory with the same name on the C drive

The DEL or ERASE commands perform the same operation; you can use either.

Command Syntax: DEL DRIVE:\PATH\FILE(S) /P

The P switch causes DOS to prompt the user with the name of the file to be deleted, to confirm that this is really his intention, before actually carrying out the deletion. If the P switch is omitted then the deletion is carried out silently.

Example 1: Prompt the user with the name of each file in the current directory that has the extension .BAK, and ask him to confirm whether it should be deleted

DEL *.BAK /P

Example 2: Delete the file HELLO.BAT from the DOCS directory

DEL C:\DOCS\HELLO.BAT

Example 3: Delete all files in the root of A

DEL A:\*.*

Whenever the wildcard character is used in this manner, the user is always reminded that all files in the directory will be deleted, and asked to confirm Yes or No.

Warning

NEVER delete the file COMMAND.COM file since it is the file which enables DOS commands to run.

Be very careful when using wildcard characters with the DEL/ERASE command, as you will not be asked to confirm the deletion of individualfiles when using it (unless you use the /P switch) and so may delete a file which you really need to keep. You should always use DIR to list the contents of the directory before you start deleting using wildcards, to see exactly what files will be affected.

The UNDELETE command, which was not available before DOS 5, attempts to undo the use of DEL. It provides a degree of protection against accidental deletion of files. UNDELETE relies on the fact that DELeting a file does not physically remove it but simply marks the area of disk concerned as available for reuse. Thus once you have deleted a file you will not see it if, for example, you execute the DIR command but providing it has not been subsequently overwritten it should be recoverable using UNDELETE.

Command Syntax: UNDELETE DRIVE:\PATH\FILE(S) /SWITCHES

Where SWITCHES are

LIST - list all files deleted which have not been subsequently overwritten
ALL - undelete all deleted files without prompting the user

Example 1: Undelete the file called HELLO.BAT which has been deleted from the A drive

UNDELETE A:\HELLO.BAT

If recoverable the dialogue will be continue something like this -

Directory: A:\
File Specifications: HELLO.BAT

Deletion-tracking file not found.

MS-DOS directory contains 1 deleted files.
Of those, 1 files may be recovered.

Using the MS-DOS directory method.

?ELLO BAT 49 1/1/96 16:23 ...A Undelete (Y/N)? Y
Please type the first character for ?ELLO .BAT: H

File successfully undeleted.

Example 2: Undelete all files that are recoverable in the current directory

DOS 5 does not have a specific command for moving files (DOS 6 does) but this can be achieved by using the COPY (or XCOPY) and DEL commands. i.e. Making copies and then deleting the originals.

Example: Move all the document files in the root directory of drive C to drive A

COPY C:\*.DOC A:

The RENAME or REN command is used to rename a file or a group of files. The file contents and the location of the renamed files remains the same.

Command Syntax: REN DRIVE:\PATH\ FILE1 FILE2

Example 1: Rename a single file

REN C:\HELLO.BAT MESSAGE.BAT

Example 2: Rename a group of files to have a common file extension

REN A:\TEMP-DIR\*.BAT *.BAK

The DOSKEY command is only available in DOS 5 and 6. Once the command is issued and the DOSKEY program installed it saves subsequent command lines typed in at the keyboard in an area, or buffer, of RAM; this in effect means that it 'remembers' previous command lines. The user can recall these lines with a few simple keysrokes instead of having to type them in again.

To start DOSKEY type

DOSKEY <return>

From this point on the command lines you input will be remembered.

You can then use the and (or F8 ) keys to view the command lines and <return> to execute your choice.

You can edit a command line you have recalled by using the and keys to position yourself within the line and using the Insert key to switch between OverWriting and Inserting text before typing in your changes. You can also clear the current command line by pressing the ESC key.

Additionally

F7 Displays a numbered list of the commands DOSKEY has stored

F9 Allows you to selects a command by number

The TYPE command is used to display the content of a textfile on screen. (If the screen displays garbled characters, with regular beeping sounds, then it is likely that the file is a non text file.) TYPE merely displays a file; it does not allow you to edit/change it.

Command Syntax: TYPE DRIVE:\PATH\ FILE

Example: Display the contents of a file called MESSAGE.BAT

The PRINT command allows you to obtain a print-out of a text file. Printers are slow devices and are often shared by more than one computer. Obviously you do not want to have to wait until your file is physically printed before being able to continue using your machine. Therefore when you execute the PRINT command your file is added to a print queue - this is a list, stored in memory, of files waiting to be printed. This 'queuing' of a file by PRINT is very quick; much quicker than the actual printing of the file. Once the PRINT command has been executed DOS is free to execute other commands even though the relevant file might not yet have been printed. You can continue working and the file will be printed, in the background, when it reaches the top of the queue.

Command Syntax: PRINT /SWITCHES DRIVE:\PATH\ FILE

Where SWITCHES are

T - Terminate printing i.e. remove all files from the print queue

C - Cancel printing of the specified file

Example 1: Print two text files

PRINT A:\TEMP-DIR\HELLO.BAK MESSAGE.BAT

Example 2: List the files in the Print Queue

PRINT

Example 3: Cancel the printing of MESSAGE.BAT

PRINT /C MESSAGE.BAT

Example 4: Empty the print queue

The COPY command can be used as a quick method of creating a small text file. The command line you use instructs DOS to copy all subsequent screen output (represented by CON:) to the file you specify, until you terminate this action and close the file by pressing Ctrl+Z (i.e. pressing the Ctrl key and before releasing it pressing the Z key) or the F6 function key.

This method of creating a file is very crude. Unlike EDIT or other editors it does not allow you to correct your mistakes as you are creating the file.

Command Syntax: COPY CON: DRIVE:\PATH\ FILE

The best way to demonstrate this use of COPY is with an example.

Type in the following. Every thing you type after the COPY line will be stored in LONG-MSG.BAT until you press Ctrl+Z or F6. If you make a mistake while typing you can abort what you have done and return to the DOS prompt by pressing Ctrl+C (i.e. pressing the Ctrl and C keys in the manner indicated for Ctrl+Z above). Use your own name where it says your name.

COPY CON: LONG-MSG.BAT
@echo off
echo.
echo GOOD DAY your name
echo.
pause
echo YOU ARE USING
ver

Then type Ctrl+Z or F6

ATTRIB enables you to assign files the properties, or attributes, of being Read Only (R), Hidden (H) and System (S) files. Each of these attributes (R, H, and S) is assigned with + and cleared with -

Command Syntax: ATTRIB + attribute DRIVE:\PATH\FILE(S) /SWITCH 
                       - attribute

Where attribute may be

R - read only file attribute (file cannot be deleted or edited but can be listed with DIR and viewed and copied)

S - system file attribute (file cannot be deleted or copied, nor is it visible with the DIR command but it can be edited)

H - hidden file attribute (same properties as S)

A file may have more than one attribute

SWITCH is

S - apply the command in all subdirectories of the path specified

Example 1: Protect the MESSAGE.BAT file from being deleted or changed - i.e. making it Read Only

ATTRIB +R MESSAGE.BAT

Try deleting or editing the file once you have added this attribute.

Example 2: Remove the Read Only attribute from a file

ATTRIB -R MESSAGE.BAT

Example 3: Hide all the batch files in the current directory

ATTRIB +H *.BAT

Use DIR to check the files have been hidden.

Example 4: Make the files visible to DIR again

ATTRIB +H *.BAT

This command can be useful for displaying the differences between two text files e.g. The current version of a file and an older version.

Command Syntax: FC /SWITCH DRIVE1:\PATH1\FILE1 DRIVE2:\PATH2\FILE2

SWITCH is

N - number the lines of the files

Example:

FC /N MESSAGE.BAT LONG-MSG.BAT

• Redirecting input and output ( <, >, >>)
• Filters e.g. MORE, SORT
• The Command Line Pipe ( | )

DOS assumes that the input to a command comes from the keyboard, and output goes to the monitor. However this flow can be redirected. Input can be read from a file rather than the keyboard, and output can be sent to a file or a printer instead of the monitor.

To read information from a file the < (less-than sign) must be used in the command line. To send information to a file or printer the > (greater-than sign) must be used.

Example 1: Save the directory listing of C to a file

DIR C: > DIR-LIST

If DIR-LIST already exist then its contents will be over written. Otherwise it is created containing the output of DIR.

The >> (double greater-than sign) is used to appendinformation to an existing file rather than overwriting it.

Example 2: Append a wide listing of the root of A and its subdirectories to DIR-LIST

DIR A: \ /W /S >> DIR-LIST

To display the contents of DIR-LIST you could use TYPE. However there may too much information to fit onto one screen. Instead you can use the < redirector to read the contents of DIR-LIST into a DOS command which will display the information one page/screen at a time.

The command is MORE

Example 3: Display the contents of DIR-LIST one screen at a time

A filter processes in some way the information input to it.

The MORE command is a filter that displays data input to it one screen at a time. As demonstrated in the last example it is often used with the < redirector.

Command Syntax: MORE < DRIVE:\PATH\ FILE

It is also commonly used with another redirector, the command line pipe (see next section).

Another filter is the SORT command which sorts a text file input to it into alphabetical order.

Example:

The pipe makes the output of one command become the inputto another, allowing you to combine commands within a command line. To pipe commands place the | (broken vertical bar key on the keyboard) between the commands concerned. This causes all output generated on the left hand side of the bar to be sent to the right hand side for processing.

Command Syntax: command-name | command-name

Example 1: Display the output of the DIR command one screen at a time

DIR | MORE

Pipes can also be used with the other redirection operators.

Example 2: Pipe a listing of the files in the root of C to the SORT command and store the output of SORT in a file called ORDERED.LST

DIR C:\ | SORT > ORDERED.LST

Additionally you can have more then one pipe within a command line.

Example 3:

PC viruses can infect the computer's memory, as well as the partition table, boot sector and files (particularly executable files) on floppy and hard disks. Different viruses attack different parts of a machine.

DOS shell, which first appeared with DOS 4 is a program that attempts to provide an easier interface to DOS. DOS shell provides a graphical front end to DOS commands allowing most of them to be executed using the mouse, with minimal keyboard input. Note that DOS shell was not provided with MS-DOS version 6.

To run the DOS shell program type DOSSHELL <return>

Once DOSSHELL is launched the first screen displays a menu bar to the top, directly beneath it a list of drives which can be accessed, and then three small windows. The windows are the Directory Tree window (in which you select a directory on the currently highlighted drive), the Files window (displaying the contents of the selected directory), and a Main window giving access to the DOS command prompt, editor, DOS Q-Basic and some disk utilities.

The screen should look similar to the figure below.

You can get help on using the DOS shell environment in the following ways -

By using the Mouse - clicking on the Help option in the menu bar

By using the keyboard - by pressing Alt+H

In both cases a pull down menu appears and you select from the menu by moving the selection bar to one of the options with either the mouse or the and arrow keys and then clicking on your chosen option or pressing <enter> to activate it. Once you have done this a dialogue box will appears corresponding to the selection made.

Another way of obtaining help is by simply highlighting the item you need help on using the mouse, and then pressing the F1 key. This has the effect of displaying a dialogue box whose content relates directly the item which was highlighted.

Alt Activates the Menu Bar
Selects a menu
<return> Activates selected menu

Basic Keys for using the windows

Tab Moves between Drives, Directories, Files and Main windows
Arrow Keys Selects option within window
<return> Activates option

There are several ways of quitting from the DOS shell environment

Press Alt+F4
Press F3
From the menu select File and choose Exit

Copyright: The University of Strathclyde Computer Centre, Glasgow, Scotland.

Permission to copy will normally be granted provided that these credits remain intact.

We'd appreciate a request before you use these notes, partly to justify distributing them, but also so we can distribute news of any updates.

These notes were written by Alastair Morrison of the University of Strathclyde Computer Centre. They form the basis of the Computer Centre's Introduction to DOS course. Alastair can be reached at Alastair.Morrison@strath.ac.uk.

Contact the Computer Centre if you're interested in finding out about or attending any of our courses.