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Windows Server 2008 Server Core : Comparing Two Files with the Comp Utility, Copying Files with the Copy Command

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11/6/2012 3:44:34 PM

1. Comparing Two Files with the Comp Utility

Sometimes it's helpful to compare two files to determine what has changed or to verify that the files are precisely the same. A common use of this technique is to compare two text files. The files could contain anything from data to application settings. Another way to use this technique is to verify that no one has tampered with executable files. Viruses and other forms of intrusion often modify executable files. Just looking at the file isn't enough in many cases to verify the damage. However, keeping a known good copy of the file on an unmodifiable source, such as a CD, and using this simple comparison utility is often enough to detect the problem. It also provides you with a way of expunging the intruder from your executables by copying the known good executable from the CD (of course, you still have to consider registry entries and other ways intruders often use to rebuild themselves). This utility uses the following syntax:

COMP [data1] [data2] [/D] [/A] [/L] [/N=number] [/C] [/OFF[LINE]]

The following list describes each of the command line arguments.


data1

Specifies the source file. You can use wildcard characters to define multiple comparisons. For example, *.DLL compares every dynamic link library in the source directory against a DLL with the same name in the destination directory.


data2

Specifies the destination file. You can use wildcard characters to define multiple comparisons. However, the source and destination specifications must compare. If the source contains just one file, then the destination will also contain one file as well.


/D

Displays the differences in decimal format (as numeric values for each character, whether or not there's an ASCII equivalent). This is the optimal setting when comparing binary or executable files.


/A

Displays the differences as ASCII characters. This is the optimal setting when comparing text files of any type (including INI or other settings files and standard data files in XML or other format).


/L

Displays the line numbers for differences. The Comp utility compares the two files line by line, where the carriage return (ASCII character 13), linefeed (ASCII character 10), or both designate the end of a line.


/N=
number

Performs a comparison of the specified number of lines in each file beginning with the first line.


/C

Performs a case-insensitive comparison of the two files. Normally, Comp considers an uppercase letter different from a lowercase letter.


/OFF[LINE]

Forces the Comp utility to compare files even when the files have the offline attribute set.


2. Copying Files with the Copy Command

The Copy command lets you create a copy of a file that exists in one directory into another directory. You can create copies on other drives, even drives that you map using Windows. In addition, this command works with nonfile devices such as the printer or keyboard. Generally, users rely on the functionality provided by Windows Explorer to move and copy files. However, the extensive list of command line switches provided by the Copy command makes it extremely flexible for use in batch commands. In addition, using some switches, such as the ASCII file transfer option for text files, can improve overall Windows copy performance. This command uses the following syntax:

COPY [/D] [/V] [/N] [/Y | /-Y] [/Z] [/L] [/A | /B ] source [/A | /B]
     [+ source [/A | /B] [+ ...]] [destination [/A | /B]]

The following list describes each of the command line arguments.


source

Defines the source of the data that you want to copy. The source is usually a file, but you can use devices as a source of data. See the "Understanding Command Line Devices" sidebar for details. You can use wildcard characters to specify the filenames. See the "Working with Wildcard Characters" sidebar for details.


destination

Defines the output location for the data that you want to copy. The destination is usually a file, but you can use devices as a destination for data. See the "Understanding Command Line Devices" sidebar for details.


/A

Copies the file as ASCII text. Using this technique improves Copy command performance. However, using this command line switch with a binary file results in data loss.


/B

Copies the file in binary mode. Many files fall into the binary category, even though you might think they are standard text files. For example, a Word DOC file is a binary file because it contains control and other characters that won't transfer well using the /A command line switch.


/D

Decrypts the destination file. This special Windows command line switch decrypts files that are encrypted using Windows encryption features. If you don't use this command line switch, the destination remains encrypted.


/L

Copies a symbolic link to the target instead of the actual file pointed to by the symbolic link when the source is a symbolic link.


/N

Creates a destination file with an 8-character filename and a 3-character file extension. Use this command line switch when you must create destination files for older systems that rely on the DOS 8.3 naming convention. Avoid using this command line switch on files with long filenames unless you really do want to create a compatible file.


/V

Verifies the destination file is the same as the source file. Writing files with verification improves reliability at the cost of performance. Windows writes the destination and then performs a file comparison when using this command line switch.


/Y and /-Y

Suppresses or enforces the prompt for overwriting destination files with the same name as the destination file provided as input to the Copy command. Use the /Y command line switch in batch files where you know the batch file will overwrite an existing destination file. The /-Y command line switch is the default, so you never need to use it.


/Z

Copies files to network destinations in a restartable mode. If the network connection fails, the Copy command gives you the option of restarting the copy from the current file position. This command line switch makes it possible to copy large files using less reliable network connections.

One of the more important features of the Copy command is the ability to combine two files. For example, you might download a large file as two file fragments from an Internet site to reduce the problems associated with downloading a single large file. Combine the two file fragments to create a complete file by typing a plus sign (+) between source files like this:

COPY FilePart1 + FilePart2 CompleteFile

When the Copy command completes, CompleteFile will contain the sum of the two file fragments.

When using the Copy command with the console, you must add an end of file marker to the input by pressing Ctrl+Z. The end of file marker appears as ^Z on screen, which signifies it as control character 26. Pressing Enter after ^Z copies the file to the destination you indicate. The end of file marker doesn't appear when you send the resulting file to the console as output. Likewise, if you want a printer to output the partial page of data you sent to it, output a Ctrl+L character to it. You can see a complete list of standard control characters at http://www.cs.tut.fi/~jkorpela/chars/c0.html.

Understanding Command Line Devices

You can access a number of devices from the command line. Some devices accept input, others output, and some accept both. These devices always reference a physical device of some type. In some cases, the device isn't attached to your machine, but it's accessible from your machine, such as a network printer. Many commands and utilities let you use a device in place of a drive letter as an argument. For example, the Copy command lets you use input from a device to create a file. You can also use a file as output to a device. Here's the standard list of command line devices.


CON

The system console, which is the combination of keyboard and monitor used to access the computer system. Input comes from the keyboard and output goes to the monitor.


PRN

The default printer. You must configure network printers to provide a port to support a command line device. The port appears on the Ports tab of the network printer's Properties dialog box. Even if your printer can provide bidirectional communication, the PRN device is only capable of output.


LPT1 through LPT4

The printer attached to the first through fourth printer (parallel) ports. The device need not physically attach to the parallel port; Windows can redirect the output to the physical device for you. You must configure network printers to provide a port to provide a command line device. The port appears on the Ports tab of the network printer's Properties dialog box. Even if your printer can provide bidirectional communication, the LPT devices are only capable of output.


AUX

The auxiliary device; the one serviced by the first serial port (COM1). It's usually better to reference COM1 directly for readability in batch files. The AUX device is a holdover from the early days of DOS.


COM1 through COM4

The communication device attached to the first through fourth serial ports. Although standard outputs for this port include modems, you can connect printers as well. The serial port can act as both an input and an output device. You can configure network printers to use a COM port instead of an LPT port using the Ports tab of the network printer's Properties dialog box.


NUL

The output doesn't go anywhere. The NUL(L) device is also known as the bit bucket.


CLOCK$

This device is supposed to access the real-time clock. In reality, the device normally doesn't work in modern systems and Windows makes no effort to provide required redirection. You should avoid using the CLOCK$ device.

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