Redirection

Redirection can be used to reassign the standard input, standard output, 
and standard error devices from their default settings (the keyboard and 
screen) to another device like the printer or serial port, to a file, or 
to the clipboard.  You must use some discretion when you use redirection 
with a device; there is no way to get input from the printer, for example. 

Redirection always applies to a specific command, and lasts only for the 
duration of that command.  When the command is finished, the assignments 
for standard input, standard output, and standard error revert to whatever 
they were before the command. 

In the descriptions below, filename means either the name of a file or of 
an appropriate device (PRN, LPT1, LPT2, or LPT3 for printers; COM1 to COM4 
for serial ports; CON for the keyboard and screen; CLIP: for the 
clipboard; NUL for the "null" device, etc.). 

Here are the standard redirection options supported by CMD.EXE (see below 
for additional redirection options using numeric file handles): 

        < filename          To get input from a file or device instead of 
                            from the keyboard 
        > filename          Redirect standard output to a file or device 
        >& filename         Redirect standard output and standard error to 
                            a file or device 
        >&> filename        Redirect standard error only to a file or 
                            device 
 
 If you want to append output to the end of an existing file, rather than 
 creating a new file, replace the first ">" in the last three commands 
 above with ">>" (i.e., use >>, >>&, and >>&>). 

 To use redirection, place the redirection symbol and filename at the end 
 of the command line, after the command name and any parameters.  For 
 example, to redirect the output of the DIR command to a file called 
 DIRLIST, you could use a command line like this: 

 
         [c:\] dir /b *.dat > dirlist
 

 You can use both input and output redirection for the same command, if 
 both are appropriate:  For example, this command sends input to SORT from 
 the file DIRLIST, and sends output from SORT to the file DIRLIST.SRT: 

 
         [c:\] sort < dirlist > dirlist.srt
 

 You can redirect text to or from the OS/2 clipboard by using the 
 pseudo-device name CLIP: (the colon is required). 

 If you redirect the output of a single internal command like DIR, the 
 redirection ends automatically when that command is done.  If you start a 
 batch file with redirection, all of the batch file's output is 
 redirected, and redirection ends when the batch file is done.  Similarly, 
 if you use redirection at the end of a command group, all of the output 
 from the command group is redirected, and redirection ends when the 
 command group is done. 

 When output is directed to a file with >, >&, or >&>, if the file already 
 exists, it will be overwritten.  You can protect existing files by using 
 the SETDOS /N1 command, the "Protect redirected output files" setting 
 available on the Options 1 page of the OPTION dialogs, or the NoClobber 
 directive in the .INI file. 

 When output is appended to a file with >>, >>&, or >>&>, the file will be 
 created if it doesn't already exist.  However, if NoClobber is set as 
 described in the above, append redirection will not create a new file; 
 instead, if the output file does not exist a "File not found" or similar 
 error will be displayed. 

 You can temporarily override the current setting of NoClobber by using an 
 exclamation mark [!] after the redirection symbol. For example, to 
 redirect the output of DIR to the file DIROUT, and allow overwriting of 
 any existing file despite the NoClobber setting: 

 
         [c:\] dir >! dirout
 

 Redirection is fully nestable.  For example, you can invoke a batch file 
 and redirect all of its output to a file or device.  Output redirection 
 on a command within the batch file will take effect for that command 
 only; when the command is completed, output will revert to the redirected 
 output file or device in use for the batch file as a whole. 

 You can use redirection if you need to create a zero-byte file.  To do so, 
 enter >filename as a command, with no actual command before the > 
 character. 

 In addition to the standard redirection options above, CMD.EXE also 
 supports the OS/2 CMD.EXE syntax: 

        n>file      Redirect handle n to the named file 
        n>&m        Redirect handle n to the same place as handle m 
 
 [n] and [m] are one-digit file handles between 0 and 9.  You may not put 
 any spaces between the n and the >, or between the >, &, and m in the 
 second form. OS/2 interprets "0" as standard input, "1" as standard 
 output, and "2" as standard error.  Handles 3 to 9 will probably not be 
 useful unless you have an application which uses those handles for a 
 specific, documented purpose, or you have opened a file with the 
 %@FILEOPEN variable function and the file handle is between 3 and 9. 

 The n>file syntax redirects output from handle n to a file.  You can use 
 this form to redirect two handles to different places.  For example: 

 
         [c:\] dir > outfile 2> errfil
 

 sends normal output to a file called OUTFILE and any error messages to a 
 file called ERRFILE. 

 The n>&m syntax redirects handle n to the same location as the previously 
 assigned handle m.  For example, to send standard error to the same file 
 as standard output, you could use this command: 

 
         [c:\] .dir > outfile 2>&1
 

 Notice that you can perform the same operations by using standard CMD.EXE 
 redirection features.  The two examples above could be written as 

 
         [c:\] dir > outfile >&> errfile
 

 and 

 
         [c:\] dir >&outfile