DOS CMD redirection operation

The command redirection operator allows you to use the redirect operator to reset the command input and output data streams from the default location to a different location. The position of the input or output data stream is the handle. The following table lists the available handles. The numerical code description of handle handle STDIN 0 Keyboard input STDOUT 1 output to the command Prompt window STDERR 2 Error output to command Prompt window UNDEFINED 3-9 These handles are defined separately by the application and are specific to each tool. The number 0 to 9 represents the first 10 handles. You can use the command Cmd.exe to run the program and put the first 10 of the program Any redirect in the handle. To specify the handle you want to use, type the handle in front of the redirection operator Digital. If no handle is defined, the default < redirect input operator is 0, and the default > redirect Output The operator is 1. After you type the > or < operator, you must specify where you want to read or write data. can specify The file name or another existing handle. To specify a redirect to an existing handle, use the WITH (&) character, followed by the handle number to be redirected (for example, & handle #). For example, the following command redirects the handle 2 (that is, STDERR) to the Handle 1 (i.e. STDOUT): 2>&1 The following table lists the operators that can be used to redirect input and output data streams. Redirection operator Description > writes the command output to a file or device, such as a printer, instead of writing it in a command prompt window or handle. < reads the command input from the file instead of from the keyboard or handle. >> adds the command output to the end of the file without deleting the information in the file. >& writes the output of one handle to the input of another handle. <& reads the input from one handle and writes it to another handle output. | Reads the output from one command and writes it to the input of another command. Also known as pipelines. By default, you can send command input (that is, the STDIN handle) from the keyboard to Cmd.exe and then by the Cmd.exe sends the command output (that is, the STDOUT handle) to the command Prompt window. redirect Input (<) To redirect keyboard input to a file or device, use the < operator. For example, to get from File.txt Enter the sort command, type: Sort<file.txt The contents of the File.txt are displayed in a command prompt window as an alphabetical list. The < operator can open a specified file name with read-only access. Therefore, you cannot use this operator to write to a file Information. For example, if you start a program with &LT;&AMP;2, all operations that attempt to read handle 0 will fail because the sentence Handle 2 was originally opened with write-only access. Attention 0 is the default handle to the < redirect input operator. Redirected Output (>) Almost all commands send output to the command prompt window. Even if the output is sent to a drive or printer The command also displays messages and prompts at the Command Prompt window. To redirect output from a command prompt window to a file or device, use the > operator. There are many commands that you can Use this operator. For example, to redirect the dir output to Dirlist.txt, type: Dir>dirlist.txt If Dirlist.txt does not exist, Cmd.exe will create the file. If Dirlist.txt exists, Cmd.exe The output from the dir command is replaced with the information in the file. To run the Netsh routing dump command, and then send the output to Route.cfg, type: netsh routing dump>c:\route.cfg The > operator can open a specified file with write-only access properties. Therefore, you cannot use this operator to read a file. For example, if you use the redirect >&0 Launcher, all operations that attempt to write to handle 1 will fail because Handle 0 was originally opened with read-only access. Attention 1 is the default handle to the > redirect Output operator. Copy handle The redirect operator & can copy output or input from one specified handle to another specified handle. For example To send the Dir output to File.txt and send the error output to File.txt, type: Dir>c:\file.txt 2>&1 When you copy a handle, you can copy all the attributes of the original state of the handle. For example, if a handle has write-only access to the property, all copies of the handle have a write-only access property. A handle to a property with read-only access cannot be Copy to another handle with a write-only access property. Redirecting inputs and replicas using the & operator To use the redirect input operator (<) with the copy operator (&), the specified file must already exist. If the input file exists, Cmd.exe opens the file as read-only and then takes the characters contained in the file as The input is sent to this command (as in the keyboard input). If a handle is specified, Cmd.exe the specified handle Copied to the system's existing handle. For example, to open File.txt in the form of a handle 0 input read (that is, STDIN), type: <file.txt To open File.txt and send the output to a command prompt window (that is, STDOUT) after the content is sorted, type: Sort<file.txt To find File.txt, then redirect handle 1 (that is, STDOUT) and handle 2 (that is, STDERR) to Search.txt, type: FindFile File.txt>search.txt 2<&1 To copy the user-defined handle 3 as a handle 0 input read (that is, STDIN), type: <&3 REDIRECT Output and replication using the & operator If the output is redirected to a file and an existing file name is specified, Cmd.exe will open the file as write-only and Cover the contents of the file. If a handle is specified, Cmd.exe copies the file to the existing handle. To copy the user-defined handle 3 to handle 1, type: >&3 To redirect all output including handle 2 (that is, STDERR) from the ipconfig command to Handle 1 (that is, STDOUT), and then redirect the output to Output.log, type: Ipconfig.exe>>output.log 2>&1 Append output using the >> redirect operator To add output from the command to the end of the file without losing any information that already exists in the file, use two consecutive The greater than sign (i.e. >>). For example, the following command can append a list of directories generated by the dir command to the Dirlist.txt file: Dir>>dirlist.txt To append the output of the netstat command to the end of Tcpinfo.txt, type: Netstat>>tcpinfo.txt Using the pipe operator (|) The pipe operator (|) can extract the output of one command (STDOUT by default) and then import it into another The input of a command (by default, STDIN). For example, the following command categorizes the directory: Dir | Sort In this example, two commands are started at the same time, but then the sort command pauses until it receives the DIR command Output. The sort command uses the output of the dir command as input and then sends the output to the Handle 1 (that is, STDOUT). Merging commands with the redirect operator You can create a custom command by merging filter commands with other commands and file names. For example, you can use the The following command stores the file name containing the string "LOG": dir/b | Find "LOG" > Loglist.txt The output of the dir command is sent through the Find filter command. File name containing the string "LOG" as the file name Lists (for example, NetshConfig.log, LOGDAT.SVD, and Mylog.bat) are stored in the file The Loglist.txt. To use multiple filters in the same command, separate the filters with a pipe (|). For example, the following command will Search each directory on drive C to find the file name that contains the string "LOG", and in the Command Prompt window Show one screen at a time: Dir c =/s/b | Find "LOG" | More The Pipeline (|) can be used to direct the Cmd.exe to send the dir command output through the Find filter command. The Find command selects only the file name that contains the string "LOG". The more command can be displayed by the Find command selection File name (one screen at a time in the Command Prompt window). For more information about filter commands, see Use a filter.