Mantas Wills DOS
User Note
Summary: DOS is the operating system for the IBM PC and compatible machines. The most common variety is MS-DOS from Microsoft. Features up to MS-DOS version 5 are covered, and new features introduced in version 6 are described.
1. Introduction 1 2. The DOS File System 1 . 2.1 File Names and Extensions 2 . 2.2 Disk Drive Letters 2 . 2.3 Directories 3 . 2.4 Identifying Files 4 . 2.5 Global Filename Characters 4 . 2.6 Paths and Pathnames 4 3. Entering DOS Commands 5 . 3.1 Internal Commands 5 . 3.2 External Commands 5 . 3.3 Repeating Commands 6 4. Handling Files 6 . 4.1 Displaying a List of Files 6 . 4.2 Displaying the Contents of a File 7 . 4.3 Renaming Files 7 . 4.4 Deleting Files 8 . 4.5 Copying Files 8 . 4.6 Moving Files 9 . 4.7 Printing Files 9 . 4.8 Creating and Changing Files 10 5. Handling Directories 10 . 5.1 Moving Between Directories 11 . 5.2 Displaying the Contents and Structure of Directories 11 . 5.3 Making Directories 12 . 5.4 Removing Directories 12 . 5.5 Copying Directories 12 6. Formatting Disks 13 7. Copying and Backing Up Disks 14 8. MS-DOS Version 5 15 9. MS-DOS Version 6 16 10. Using DOS from Windows 16
DOS provides the most popular operating environment on IBM PCs and IBM PC-compatible microcomputer systems. This document describes the most useful DOS commands. The word DOS is used for convenience to cover Microsoft MS-DOS, IBM PC-DOS and Novell DOS.
Most of the information in this document is applicable to MS-DOS versions 3.3, 5 and 6, with exceptions noted in the text (there was a version 4, but it was quickly superseded). The main new facilities found in MS-DOS versions 5 and 6 are summarised in Sections 8 and 9. If you are not sure which version of DOS you are running, type
VER
at the DOS prompt.
In order to understand how files are referred to on a PC, you need to know the meaning of the following terms:
These are described in more detail below.
A file is identified by a filename, optionally followed by a dot and a filename extension, e.g.
EXEC.BAT THESIS.DOC MYPROG3.FOR
The filename may contain up to eight characters, and the extension may contain up to three characters. Filenames and extensions may contain any of the following letters and symbols:
A-Z a-z 0-9 ! # $ % ^ & ( ) _ - { } @ ~ #
However, it is common practice to use only letters and numbers for most purposes. It is possible to create files that have no filename extension, but you are recommended to always include one that is appropriate to the content of the file. Some programs expect files to have a particular file extension. For example, files stored by the Microsoft Word word-processing program normally have file extension DOC. Some common filename extensions are listed below:
Disk drive letters are usually followed by a colon (:). A single diskette drive has drive letter A: and a hard disk has drive letter C:. If the PC has a second diskette drive then this is B:. Diskettes are often referred to as floppy disks. If a PC is connected to a network, then the network directories will be identified by one or more other drive letters such as F:, N: or Q:.
When using a command, you may need to type a drive letter before the filename to tell DOS where to find the disk that contains a file. If the drive letter is omitted when you type a filename, DOS automatically searches for the file on the disk in the default drive, i.e. the disk currently being used.
To let you know that it is ready to receive a command, DOS displays a prompt that starts with the current drive letter and ends with a greater-than sign (>). To switch to another drive, type the new drive letter followed by a colon. For example, if the original DOS prompt is
C:\>
then type
A:
to specify that you want to work from the floppy disk. This will produce a new prompt:
A:\>
This indicates that the A: drive is now the default drive. DOS will search this drive first to find any filenames that you type, unless you specify another drive. The DOS prompt usually includes the current directory, and if it does not it can be modified to do so, e.g.
C:\JULY>
where JULY is the directory name. The command to set this prompt is:
PROMPT=$P$G
If there is no current directory then a backslash is shown before the > sign.
Each disk contains a file directory, which is a table of contents for the disk. It contains the names of the files stored on the disk, their sizes, and the date they were last modified. As the number of files in a directory grows, it is usual to organise the files into categories. You can use directories to group associated files together. A directory can contain files and other directories (referred to as subdirectories), which in turn may contain further subdirectories. Keeping related files in directories makes it easier to locate a particular file.
When a disk is formatted by DOS (see Section 6) a root directory or first-level directory is created. There is a limit to the number of entries in the root directory of a disk, but subdirectories may contain any number of entries, limited only by the amount of available space on the disk. The root directory is represented by a backslash (\).
Each disk drive has a current directory. DOS will remember which directory is current on each of your drives, even when you are not accessing them.
A parent directory is any directory that contains subdirectories. The parent directory entry and the current directory entry are automatically created by DOS whenever a directory is created. DOS uses the shorthand names '.' to indicate the current directory, and '..' to represent the parent directory (i.e. one level up). Some examples of specifying directories are shown below:
In order to refer to a particular file on a disk, at least a filename must be given. Depending on the circumstances it may also be necessary to give a disk drive letter, a directory name and a filename extension. For example, a file called LETTER.DOC in a directory called JULY on disk C: may be identified in any of the following ways:
Note that it is possible to have subdirectories within directories, in which case two or more directory names may have to be given in order to uniquely identify a file.
You can use the following global filename characters in some DOS commands (COPY, DEL, REN and DIR) to refer to a group of files by a general name, rather than specifying each file individually:
These are often known as wild-card characters. They may be used in the filename or the filename extension or both. For example:
You should take great care when using wild-card characters and any filename extension with DEL or REN, as several files can easily be deleted or renamed with a single command.
When DOS is required to locate a program or batch file, and a directory is not specified, DOS searches only the current directory of the default drive. To refer to a file in a directory other than the current directory, DOS must be given the name of the directory and the filename, i.e. DOS is given the pathname to the file. A pathname is a sequence of directory names followed by a filename. Each directory name in a pathname is separated from the previous one by a backslash (\). The sequence of directory names is referred to as the path. A pathname may contain any number of directory names up to a total length of 63 characters. If a pathname begins with a backslash, DOS searches for the file beginning at the root directory. For example, the pathname
\EXAMPLES\WORD5\MEMO.DOC
refers to the file MEMO.DOC in the subdirectory WORD5 which is in the directory EXAMPLES.
The PATH command is used to set a command search path, i.e. to tell DOS which directories to search after searching the current directory. For example, the command
PATH C:\USER\PETE
tells DOS to search the subdirectory PETE in the directory USER on the C: drive for any commands (that are not internal DOS commands) which it can not find in the current directory. This path will remain active until you switch the machine off or set another path. Note that it is possible to give several directories in a single PATH command, by including a semicolon between pathnames, e.g.
PATH C:\DOS;D:\WINDOWS;C:\MYPROG
The paths will be searched in the order given in the PATH command. It is advisable to always include the drive letter in a path.
It is possible to set a prompt and a search path every time a system is used, by including a PATH command in a file called C:\AUTOEXEC.BAT. Any commands included in AUTOEXEC.BAT will be carried out each time the PC is switched on. For more details of the use of paths and AUTOEXEC.BAT, see User Note 510, Getting the Best from Your PC.
DOS commands may be typed in upper-case or lower-case letters (or a combination) in response to the DOS prompt. To submit a command, type it and press the Enter key. For example, to enter the command DIR, type
DIR
and press Enter. There are two types of DOS command: internal commands and external commands.
The most commonly used DOS commands are internal commands, e.g. DIR, COPY, DEL, REN, CD, MD, RD and TYPE. These commands are loaded into memory when a PC is switched on and are carried out immediately they are typed.
Any filename with an extension of COM, EXE or BAT is considered an external command. For example, files such as FORMAT.EXE and DISKCOPY.EXE are external commands. Before DOS can run an external command, it must read the command into memory from disk. When you give an external command, DOS immediately checks your current directory to find that command. If it is not found, you must tell DOS which directory the external command is in by typing the pathname before the command, e.g.
C:\DOS\FORMAT A:
where the FORMAT command is in the directory DOS on drive C:.
If you make a mistake when typing a DOS command you will get an error message such as:
Bad command or file name
You can then simply retype the command correctly, but for long commands this can be irritating. An easier method is to press the right arrow key or F1 key. Each time you do this a letter of the previous command will be displayed. When you get to the incorrect letter you can simply type the correct letter instead of pressing the right arrow key. You can also use the Insert and Delete key to make changes to the command. When the correct command is displayed, press Enter as usual to submit it.
In DOS 5 and later versions there is a command called DOSKEY that allows you to see and repeat several earlier commands by pressing the up arrow and down arrow keys. DOSKEY may already be available on your system. If not, you can type the command DOSKEY to make it available, then press up arrow to recall commands.
This section gives examples of some commonly used DOS commands for controlling files. Most commands have a number of possible parameters. Details of the full format of commands are given by the HELP command (in DOS 5 and later versions).
The DIR command is used to list all the files in a directory or a specified group of files. You can use the wild-card characters ? and * in the filename and extension with the DIR command. If either the filename or filename extension are omitted, the default is *. The /P parameter is very useful as it makes the directory display stop scrolling when the screen is full. For example:
DIR
displays all the directory entries for the current directory of the default drive.
DIR C:
displays all the directory entries for the current directory on drive C:.
DIR /P
lists all the directory entries in the current directory on the default drive, one screenful at a time. Press any key to resume scrolling the display, or Ctrl and C to interrupt it.
DIR A:FILE1.* /S
lists the directory entries for all files named FILE1 in the current directory and its subdirectories on drive A: (regardless of their filename extension).
The information provided in the directory listing includes the disk identification and the amount of free space left on the disk. The display line for each file includes its size in bytes (characters) and the date and time that the file was last updated. Entries that name other directories are clearly identified by <DIR> instead of the size of the file. You can display a large number of directory entries on the screen at one time by using the /W parameter, e.g.
DIR /W
In this case the file names and extensions are listed across the screen, but the file size and date are not included, and directories are shown in square brackets.
The TYPE command may be used to display the contents of a file on the screen. Wild-card characters are not allowed in the filename or extension. To stop the display disappearing off the screen, press the Ctrl and S keys together or use MORE as shown below. For example:
TYPE D:MYFILE.BAT
displays the file MYFILE.BAT, which is held in the current directory on drive D:.
TYPE \SUBD\PROG.FOR
displays the file PROG.FOR, which is held in the directory SUBD on the default drive.
TYPE HOLIDAY.DAT | MORE
displays the file HOLIDAY.DAT in the current directory one screenful at a time. To see the next screenful, press any key. To interrupt the display, press Ctrl and C.
The MORE command may be used as an alternative to TYPE with MORE, e.g.
MORE < HOLIDAY.DAT
Note that MORE is an external DOS command and so the MORE command or pipe will only work if the file MORE.COM is in a directory on the current path.
Only text files are displayed by TYPE or MORE in a legible format. Other files, such as word processor files or program files, appear unreadable due to the presence of non-alphabetic and non-numeric characters.
The REN or RENAME command is used to change the name of a file. The name of the first file specified is changed to the second one. A path can be specified only with the first file name; the file will remain in the same directory after its name has been changed. The wild-card characters ? and * may be used with this command. For example:
RENAME A:LETTER.TXT MEMO.TXT
changes the name of the file LETTER.TXT on drive A: to MEMO.TXT.
REN *.TXT *.DOC
changes the filename extension of all files with an extension of TXT in the current directory from TXT to DOC.
The DEL or ERASE command is used to delete a file or group of files from a disk. You should take great care when using the wild-card characters ? and * with this command, as several files can easily be erased with a single command. For example:
DEL *.TXT
deletes all files with filename extension TXT in the current directory.
DEL A:FILE1.DAT
deletes the file FILE1.DAT from the disk in drive A:.
ERASE C:\LEVEL1
deletes all files from the directory LEVEL1 on drive C:.
ERASE *.*
deletes all files in the current directory. The following message is displayed as a precaution:
Are you sure (Y/N)?
Type Y if you really do want to erase all the files.
DEL FILE1 /P
prompts before it deletes the file. This parameter was not available in DOS version 3.3.
DOS provides three main commands for copying files:
The COPY command is used to copy a file or group of files from one disk to another or from one directory to another. The wild-card characters ? and * may be used with this command. The file to be copied (the source file) is named first. If the second parameter is a directory, files are copied into that directory without changing their names. For example:
COPY ACCOUNTS.WKS C:\OCT\ACC.WKS
copies the file ACCOUNTS.WKS from the current drive and directory to the file ACC.WKS in the directory OCT on drive C:.
COPY B:MYPROG.FOR A:
copies the file MYPROG.FOR from drive B to drive A: with no change in the filename or extension.
COPY A:*.* C:
copies all files in the current directory on drive A: to drive C, with no change in the filename or extension. The names of the files will be displayed as they are copied.
In MS-DOS version 6 the MOVE command was introduced, to allow you to move files from one directory to another, instead of having to copy and delete them. Its usage is very similar to COPY. For example,
MOVE *.DOC C:\DOCS
would move all DOC files from the current directory to the DOCS directory on drive C:. In earlier versions of DOS, files can be moved by using COPY to copy a file, then DEL remove the original one.
There are a number of ways of printing information on paper if you have a printer connected to a PC:
The PRINT command is not recommended as it is actually a 'terminate-and-stay-resident' program (TSR), which means that there is less memory available in a machine after using it. PRINT can also cause problems when using a PC connected to a network, and so should generally be avoided from networked PCs.
DOS uses the keywords PRN, LPT1, LPT2 and LPT3 to refer to a printer connected to the PC. If there is only one printer this may be referred to as either PRN or LPT1. If there are two printers available they are usually referred to as LPT1 and LPT2. These keywords may be used as parameters to DOS commands to direct output to a specified printer. For example:
COPY A:\READY.TXT LPT1
prints the contents of the file READY.TXT from the disk in drive A:.
DIR \PRICES >PRN
prints a list of all entries in the directory PRICES.
TYPE C:AUTOEXEC.BAT >LPT2
prints the contents of the file AUTOEXEC.BAT on the printer connected to the second parallel port.
There are several ways in which files may be created under DOS, for example:
The procedure for copying files is described in Section 4.5.
If you use a word processor such as Microsoft Word to create and amend files, you should be aware that the files created will be stored in a format specific to that program. This presents no problems for files containing text, but it is not normally appropriate for files containing data, commands or programs. For creating or amending these types of files there are two main options:
EDIT EXPT.DAT
You can then type or amend the contents as you would expect, using the cursor and backspace keys to move around the file. To quit the editor, press Alt and F then X. You will be prompted whether or not you wish to save the file.
If you have an earlier version of DOS, the EDIT command is not available. There is a line editor called EDLIN but this is awkward to use. There are other alternatives, such as MicroEMACS or PC-Write, which are not part of DOS but are freely available and run under DOS 3. Contact Computing Service Advisory for details.
The use of directories for storing files makes it easy to organise large quantities of information in a meaningful way. DOS always looks in the current directory to find any files whose names are entered without specifying a path.
The CD command (short for CHDIR) is used to change the current directory. For example:
CD \
changes the current directory of the default drive to its root directory.
CD ..
changes the current directory from a subdirectory to its parent directory.
CD TUFNELL
changes to the subdirectory TUFNELL within current directory.
CD C:\LEVEL1\LEVEL2
changes the current directory of drive C:to the path \LEVEL1\LEVEL2. The backslash (\) tells DOS to start at the root directory.
CD
displays the current directory path of the default drive.
To display the contents of a directory, use the DIR command as described in Section 4.1. For example, to display the files in the directory EXAMPLES, you could first type
CD \EXAMPLES
to change to the EXAMPLES directory, then type
DIR
to display the list of files in that directory. Alternatively, you could display all the files in EXAMPLES from within the root directory, one screenful at a time, by typing:
DIR \EXAMPLES /P
Once you have a significant number of directories and subdirectories, it is easy to forget where a file is located. In this case you can use DIR with the /S option as well, e.g.
DIR /S /P
would display all files in all subdirectories of the current directory. Note that the /S option is not available in DOS version 3.
It is possible to change the default operation of the DIR command by setting a variable in your AUTOEXEC.BAT file. For example, if you added the line
SET DIRCMD=/O:-D-G/P
to AUTOEXEC.BAT, then whenever you just typed DIR files would be listed in date order one screen at a time, with the most recently created or changed file shown first.
The MD command (short for MKDIR) is used to create a directory or subdirectory on a specified disk. DOS automatically makes the '.' and '..' entries in a new directory, representing the current directory and the parent directory respectively. Directory names may contain up to eight characters, including any of the same symbols as filenames (see Section 2.1). For example:
MKDIR \REPORTS
creates the subdirectory REPORTS under the root directory of the current drive.
MD LEVEL42
creates the subdirectory LEVEL42 within the current directory or subdirectory. The absence of a leading backslash causes DOS to begin at the current directory.
Note that directory names can include extensions. For example,
MD N:\WIN4WG-3.11
creates the directory WIN4WG-3.11 on drive N.
The RD command (short for RMDIR) is used to remove a directory from a disk. A directory can be removed only if it is empty, i.e. if the special entries '.' and '..' are the only two entries displayed when the DIR command is issued. The root directory and the current directory cannot be removed. For example:
RMDIR BRAIN
removes the directory BRAIN from the current directory.
RD C:\SEP94\DATA
removes the subdirectory DATA from the directory SEP94 on the C: disk.
If you have DOS version 6.0 or later, a new command, DELTREE, allows deletion of a directory and all of its files and subdirectories. Note, however, that this command could potentially delete most of the files on the disk, so it should be used with great care.
The XCOPY command may be used to copy files and directories, including the contents of any subdirectories that exist. There are a number of optional parameters to the command, but the most useful ones are /S and /P. For example:
XCOPY A: B: /S
copies all the files and subdirectories on the disk in drive A: to the disk in drive B.
XCOPY C: A: /S /P
copies files and subdirectories from the current directory on drive C:to the disk in drive A, but prompts with (Y/N)? before each file, allowing you to confirm whether you want the file to be copied.
The FORMAT command is used to prepare a disk for use. FORMAT initialises the disk in the designated drive, analyses the entire disk for any defective tracks, and prepares the disk to accept DOS files by initialising the directory. When a disk is new, it must be formatted before you can use it. If you format a disk that contains information, the information is destroyed. Because of this you should be very careful before you decide to format any disk.
Most models of PC have disk drives that use high-density 3.5" disks, which can store 1.44 Mb. Some new models have disk drives that handle disks which can store 2.88 Mb. Older models of PC have disk drives that use 5.25" disks storing either 360 Kb or 1.2 Mb, or standard-density 3.5" disks which can store 720 Kb of information. Some models have two or three different types of disk drive. A disk drive will try to format a disk to its maximum design capacity unless told otherwise. For example, if you type
FORMAT A:
to format a 3.5" disk, DOS will attempt to format the disk for either 720 Kb or 1.44 Mb, depending on whether drive A: is a standard-capacity (720 Kb) or high-capacity drive (1.44 Mb). This can cause a problem if you want to format a standard-density disk in a high-capacity drive (e.g. in order to transfer information to a PC that is only equipped with standard-capacity disk drives). If you are sure that you want to format a standard-density disk in a high-capacity drive, use one of the following commands, depending on the size of disk:
For a 3.5" disk, use the command:
FORMAT A: /N:9 /T:80
This command limits the number of sectors and tracks on the disk to values suitable for a standard-density 720 Kb disk. A standard-density disk formatted to 720Kb in a high-capacity disk drive should be perfectly reliable.
For a 5.25" disk, use the command:
FORMAT A: /4
This may work but is not guaranteed; the IBM DOS manual states 'this parameter is intended to allow use of double-sided diskettes in high capacity drives. However, the diskettes formatted with the /4 parameter specified may not be read reliably or written in a double-sided drive'.
You should ensure that you do not under any circumstances attempt to format a standard-density disk as high-density, or vice versa. If you do this you will risk losing all the data subsequently written to the disk, and will encounter problems when trying to use the disk on different machines.
When a FORMAT command is issued, the system displays the message:
Insert new diskette for drive A: and strike ENTER when ready
The formatting process takes several seconds. When it is complete, you will get a message showing the number of bytes of space available on the disk followed by the question Format another (Y/N)?. Type N to end the FORMAT command or Y to format another disk.
When you use a PC, you will normally be responsible for keeping a secure copy of all your own files on your own fixed disk or diskettes or both. Disks are susceptible to errors and damage, so any important files should be stored in duplicate (at least) with the copies on another disk. Please remember that the secure storage of your files is your own responsibility. In many cases files can not be recovered from corrupt disks, and files which have been accidentally deleted cannot necessarily be recovered.
Each time you make major changes to a file you should copy the file from the disk you are working with to another disk, so that you always have at least one back-up copy available. You may copy individual files with the COPY command or copy whole directories and subdirectories with the XCOPY command, as described in Sections 4.5 and 5.5. In addition, the DISKCOPY and BACKUP commands are particularly useful for copying complete disks. These are described below.
DISKCOPY may be used to copy the contents of one disk (the source) to another (the target), provided that the two disks have the same format. If necessary the target disk is formatted during the copy. For example, the command
DISKCOPY A: B:
will copy the entire contents of the disk in drive A: to the disk in drive B.
If you specify the same drive, a one-drive copy operation will be performed and you will be prompted to insert different disks at the appropriate times. In this case remember that 'SOURCE' means the original disk, and 'TARGET' means the copy you are creating. Before beginning the operation, you should always make sure that the source disk is write-protected (which means that you can not store any new information on it), and so if you do make a mistake and insert the wrong diskette you will get a warning message but will not lose any information. (To write-protect a 3.5" disk, slide the black tab in the corner so that so you can see through a hole in the disk; to write-protect a 5.25" disk, cover the notch near the corner with a small sticky label.)
The procedure for one-drive copying is summarised below:
DISKCOPY A: A:
The system displays the message:
Insert SOURCE diskette in drive A: Press any key when ready
Insert TARGET diskette in drive A: Press any key when ready
Copy another diskette (Y/N)?
In DOS 3 and 5, the BACKUP command may be used to make a complete security copy of a fixed disk to a series of diskettes. For example, the command
BACKUP C: A: /S
will copy all files in all directories and subdirectories from the C:disk to the diskettes in drive A:. You should have plenty of formatted diskettes before using this command, as in some versions of DOS the BACKUP command does not allow you to format diskettes. In MS-DOS version 6, the equivalent command is MSBACKUP.
New features in MS-DOS version 5 include:
New features in MS-DOS version 6 include:
Almost all new PCs are now supplied with Microsoft Windows. The use of Windows, and File Manager in particular, can save you typing DOS commands. However, for some tasks, some people find it simpler and quicker to escape to DOS. To use DOS from Windows, select the icon:
You will then normally get a full-screen DOS display and can type DOS commands as usual, though there will be less memory available for running programs. To put the DOS screen in a Window, press Alt and Enter. To return from DOS to Windows, type:
EXIT
The main MS-DOS reference is the HELP command. For introductory information on using Windows, see User Note 521, Using Microsoft Windows. For information on PC hardware, advice on PC usage, details of command files, batch files and paths, further information about formatting and backing up disks, network usage, terminal emulation and other useful information, see User Note 510, Getting the Best from Your PC. Both these documents are available from the Computing Service. If you have any queries about using DOS, contact Computing Service Advisory (ext 4831 or electronic mail to adviser@compserv.gla.ac.uk).