Sunday, October 17, 2010

Basic DOS commands

Occasionally on your Windows computer, you may need to perform a procedure by typing in commands at the 'Command Prompt'. Entering commands in this way allows you to bypass the Windows graphical user interface and communicate directly with the operating system. You are most likely to need to work in this way if you get an infection and have to disinfect your computer from the command line, for example, using one of the Sophos Resolve tools, or SAV32CLI or SWEEP.EXE.

To communicate through the Windows command line, you will need to use MS-DOS commands. This article lists some basic DOS commands that you are likely to find useful when working from the command line, but there are many more available. To find out more about MS-DOS, consult a book, online dictionary or encyclopedia, or other specialist publication.
Command and UsageExamples
Change file attributes. '+' adds an attribute, '-' removes it. Attributes are: A=archive; R=read only; S=system; H=hidden.
All these attributes will be removed from virus.exe.
Go to the C: drive. Similarly A: and D: etc.
Change directory. When you change directory, the prompt changes, showing the path of the directory you are currently in.
Note, directory is the term used by DOS for what Windows calls a folder.
CD\ takes you to the top of the directory tree (typically to C:) .
CD.. moves you one level up the directory tree (i.e. up towards the root directory).
CD <DIRECTORYNAME> takes you to that directory. You can use one or more subdirectory names, separated by \ e.g.
CD WINNT\Media takes you to the directory C:\WINNT\Media
To change to another path, type the full path with slashes. e.g.
Clear the screen.
Delete one or more files in the current directory. Can be used with the '*' and the '?' wildcards.
DEL *.* will delete ALL files in the current directory, USE WITH CAUTION.
(Note: DEL cannot be used to delete directories. Use RD to remove a directory.)
DEL <VIRUS.EXE> deletes virus.exe
DEL *.JPG will delete all files with the extension JPG.
DEL MY*.* will delete all files beginning with MY and with any extension.
DEL MY??.* will delete files that are 4 characters long and begin with MY and with any extension.
Displays the contents of a directory (folder).
Note, directory is the term used by DOS for what Windows calls a folder.
These switches can be combined, so DIR /W /P will return multiple rows listing a page at a time.
You can use the '*' and the '?' wildcards to search for a particular file. The ? character represents ONE character, and the * character represents multiple characters.
DIR *.* lists all the files in a directory.
DIR displays all files and folders in the current directory. Folders are indicated in the list by <DIR>.
Files are usually listed by name.
DIR /P displays the contents a page at a time, i.e. as many as will fit in your command line window. Press any key to display the next page.
DIR /W displays the files/folders in multiple rows. This view gives less information per file.
DIR *.JPG displays all files with the extension JPG in the current directory and all subdirectories.
DIR MY??.* displays all files beginning with MY, exactly 4 characters long, and with any extension.
DIR /S lists the contents of all subdirectories.
DIR /AH displays all hidden files.
Runs DOS EDIT (a simple text editor). Useful for editing batchfiles and viewing logs. This command requires QBASIC.EXE to be present.
EDIT <VIRUSLOG.TXT> opens the file viruslog.txt and allows you to edit it.
EDIT <NEWFILE.TXT> creates a new file called newfile.txt and opens it up for you to edit.
Displays DOS Help. For help on an individual command, type HELP then the command for which you want more information.
HELP DIR displays information on the DIR command.
Make directory. Creates a new directory below the current one. (The command can also be written as MKDIR)
MD <NEWDIR> creates a new directory called Newdir.
Prints the specified file (if the printer is supported in DOS - many are not).
Remove directory. Removes a subdirectory of the current directory. The directory you want to remove must be empty of all files. (The command can also be written as RMDIR)
Rename a file. You must use the full file name including the suffix.
Displays the contents of a file on the screen. If you use this command on a file which is not a text file, the display will be unintelligible. Use with "|MORE" to display the text on a page by page basis, and prevent it scrolling off the screen. "|" is a pipe character.
When you run a DOS command, output is usually sent to the screen. Use > to redirect output from the screen to a file. It runs the command preceding the >, creates a file in the current directory with the name you specify, and sends the information/output returned by the command, to that file.
e.g. SWEEP > REPORT.TXT The details of any infected files reported by SWEEP are sent to a file called REPORT.TXT.

If need to append the output to a file, just use ">>".

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