Section 6.3. Wildcards, Pipes, and Redirection

6.3. Wildcards, Pipes, and Redirection

In addition to the various command-line parameters used by each of the commands documented in this chapter (and the components documented in Chapter 4), there are certain symbols used on the command line that have special meaning. Table 6-1 shows these special symbols and what they do. They must be used in conjunction with other commands (they don't stand alone) and can be used in the Command Prompt window, in Start Run, and in any Address Bar.

Table 6-1. Special symbols on the command line

Symbol	Description
*	Multiple-character wildcard, used to specify a group of files.
?	Single-character wildcard, used to specify multiple files with more precision than *.
.	One dot represents the current directory; see "cd or chdir".
..	Two dots represent the parent directory; see "cd or chdir".
... (three dots)	Three dots represent the grandparent directory; see "cd or chdir".
\	Separates directory names , drive letters , and filenames. By itself, \ represents the root directory of the current drive.
>	Redirects a command's text output into a file instead of the console window; existing files will be overwritten.
>>	Redirects a command's text output into a file instead of the console window, appending existing files.
<	Directs the contents of a text file to a command's input; use in place of keyboard entry to automate interactive command-line applications.
	Redirects the output of a program or command to a second program or command (this is called a "pipe").

6.3.1. Examples

The following examples demonstrate some uses of wildcards, pipes, and redirection:

*.*

Specify all files with all extensions.

professor *.*

Specify all files (with filenames that begin with "professor") with any extension.

chap??.doc

Specify all files named "chap" followed by any two characters and with the doc extension (e.g., chap01.doc , but not chap1.doc or chap.doc ).

dir ..

List all the files in the current directory's parent.

dir > c:\ nutshell \mylist.txt

List all files in the current directory and store this listing into a file called mylist.txt rather than displaying it in the command prompt window. If the file already exists, it will be overwritten.

In addition to directing output to a file, you can direct to a device, such as NUL (an electronic void). This is useful if you want a command to run without sending output to the screen.

dir c:\ windows >> c:\nutshell\mylist.txt

Add the directory listing of the files in the c:\Windows directory to the end of the file windows.txt .

If the specified file doesn't exist, one is created. If one does exist, the output from the command is added to it, unlike with the > key, where the original contents are overwritten.

echo y del *.*

Normally, the DEL command has no prompt. However, if you try to delete all the files in a directory, del will prompt you for confirmation. To automate this command, the output of the ECHO command (here, just a "y" plus a carriage return) is "piped" into the input (commonly known as STDIN) of the DEL command.

del *.* < y.txt

Assuming y.txt contains only a letter "y" followed by a carriage return, this command has the same effect as the previous example.

sort /+12 < c:\nutshell\mylist.txt

To sort the lines in a text file ( c:\nutshell\mylist.txt ) on the twelfth character, the SORT command is fed input from the file. The output is sent to the screen, not reordered in the file.

Keep in mind that not all commands handle wildcards in exactly the same way. For example, dir * and dir *.* list the same thing , but del * will delete only files without an extension.