Windows cmd redirect output to file

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Display & Redirect Output

On this page I’ll try to explain how redirection works.
To illustrate my story there are some examples you can try for yourself.

For an overview of redirection and piping, view my original redirection page.

Display text

To display a text on screen we have the ECHO command:

ECHO Hello world

This will show the following text on screen:

Hello world

When I say «on screen», I’m actually referring to the «DOS Prompt», «console» or «command window», or whatever other «alias» is used.

Streams

The output we see in this window may all look alike, but it can actually be the result of 3 different «streams» of text, 3 «processes» that each send their text to thee same window.

Those of you familiar with one of the Unix/Linux shells probably know what these streams are:

• Standard Output
• Standard Error
• Console

Standard Output is the stream where all, well, standard output of commands is being sent to.
The ECHO command sends all its output to Standard Output.

Standard Error is the stream where many (but not all) commands send their error messages.

And some, not many, commands send their output to the screen bypassing Standard Output and Standard Error, they use the Console.
By definition Console isn’t a stream.

There is another stream, Standard Input: many commands accept input at their Standard Input instead of directly from the keyboard.
Probably the most familiar example is MORE:

DIR /S | MORE

where the MORE command accepts DIR‘s Standard Output at its own Standard Input, chops the stream in blocks of 25 lines (or whatever screen size you may use) and sends it to its own Standard Output.

(Since MORE‘s Standard Input is used by DIR, MORE must catch its keyboard presses (the «Any Key») directly from the keyboard buffer instead of from Standard Input.)

Redirection

You may be familiar with «redirection to NUL» to hide command output:

ECHO Hello world>NUL

will show nothing on screen.
That’s because >NUL redirects all Standard Output to the NUL device, which does nothing but discard it.

Now try this (note the typo):

EHCO Hello world>NUL

The result may differ for different operating system versions, but in Windows XP I get the following error message:

'EHCO' is not recognized as an internal or external command, operable program or batch file.

This is a fine demonstration of only Standard Output being redirected to the NUL device, but Standard Error still being displayed.

Redirecting Standard Error in «true» MS-DOS (COMMAND.COM) isn’t possible (actually it is, by using the CTTY command, but that would redirect all output including Console, and input, including keyboard).
In Windows NT 4 and later (CMD.EXE) and in OS/2 (also CMD.EXE) Standard Error can be redirected by using 2> instead of >

A short demonstration. Try this command:

ECHO Hello world 2>NUL

What you should get is:

Hello world

You see? The same result you got with ECHO Hello world without the redirection.
That’s because we redirected the Standard Error stream to the NUL device, but the ECHO command sent its output to the Standard Output stream, which was not redirected.

Now make a typo again:

EHCO Hello world 2>NUL

What did you get?
Nothing
That’s because the error message was sent to the Standard Error stream, which was in turn redirected to the NUL device by 2>NUL

C:\>test.bat

C:\>DIR  1>NUL

C:\>_

Ok, now that we get the idea of this concept of «streams», let’s play with it.
Copy the following code into Notepad and save it as «test.bat»:

@ECHO OFF
ECHO This text goes to Standard Output
ECHO This text goes to Standard Error 1>&2
ECHO This text goes to the Console>CON

Run test.bat in CMD.EXE, and this is what you’ll get:

C:\>test.bat
This text goes to Standard Output
This text goes to Standard Error
This text goes to the Console

C:\>_

Now let’s see if we can separate the streams again.
Run:

test.bat > NUL

and you should see:

C:\>test.bat
This text goes to Standard Error
This text goes to the Console

C:\>_

We redirected Standard Output to the NUL device, and what was left were Standard Error and Console.

Next, run:

test.bat 2> NUL

and you should see:

C:\>test.bat
This text goes to Standard Output
This text goes to the Console

C:\>_

We redirected Standard Error to the NUL device, and what was left were Standard Output and Console.

Nothing new so far. But the next one is new:

test.bat > NUL 2>&1

and you should see:

C:\>test.bat
This text goes to the Console

C:\>_

This time we redirected both Standard Output and Standard Error to the NUL device, and what was left was only Console.
It is said Console cannot be redirected, and I believe that’s true.
I can assure you I did try!

To get rid of screen output sent directly to the Console, either run the program in a separate window (using the START command), or clear the screen immediately afterwards (CLS).

In this case, we could also have used test.bat >NUL 2>NUL
This redirects Standard Output to the NUL device and Standard Error to the same NUL device.
With the NUL device that’s no problem, but when redirecting to a file one of the redirections will lock the file for the other redirection.
What 2>&1 does, is merge Standard Error into the Standard Output stream, so Standard output and Standard Error will continue as a single stream.

Redirect «all» output to a single file:

Run:

test.bat > test.txt 2>&1

and you’ll get this text on screen (we’ll never get rid of this line on screen, as it is sent to the Console and cannot be redirected):

This text goes to the Console

You should also get a file named test.txt with the following content:

This text goes to Standard Output
This text goes to Standard Error

Redirect errors to a separate error log file:

Run:

test.bat > testlog.txt 2> testerrors.txt

and you’ll get this text on screen (we’ll never get rid of this line on screen, as it is sent to the Console and cannot be redirected):

This text goes to the Console

You should also get a file named testlog.txt with the following content:

This text goes to Standard Output

and another file named testerrors.txt with the following content:

This text goes to Standard Error

CTTY NUL
ECHO Echo whatever you want, it won't be displayed on screen no matter what.
ECHO By the way, did I warn you that the keyboard doesn't work either?
ECHO I suppose that's why CTTY is no longer available on Windows systems.
ECHO The only way to get control over the computer again is a cold reboot,
ECHO or the following command:
CTTY CON

Escaping Redirection (not to be interpreted as «Avoiding Redirection»)

Redirection always uses the main or first command’s streams:

START command > logfile

will redirect START‘s Standard Output to logfile, not command‘s!
The result will be an empty logfile.

A workaround that may look a bit intimidating is grouping the command line and escaping the redirection:

START CMD.EXE /C ^(command ^> logfile^)

What this does is turn the part between parentheses into a «literal» (uninterpreted) string that is passed to the command interpreter of the newly started process, which then in turn does interpret it.
So the interpretation of the parenthesis and redirection is delayed, or deferred.

command > logfile

START batchfile

Some «best practices» when using redirection in batch files:

• Use >filename.txt 2>&1 to merge Standard Output and Standard Error and redirect them together to a single file.
  Make sure you place the redirection «commands» in this order.
• Use >logfile.txt 2>errorlog.txt to redirect success and error messages to separate log files.
• Use >CON to send text to the screen, no matter what, even if the batch file’s output is redirected.
  This could be useful when prompting for input even if the batch file’s output is being redirected to a file.
• Use 1>&2 to send text to Standard Error.
  This can be useful for error messages.
• It’s ok to use spaces in redirection commands.
  Note however, that a space between an ECHO command and a > will be redirected too.
  DIR>filename.txt and DIR > filename.txt are identical, ECHO Hello world>filename.txt and ECHO Hello world > filename.txt are not, even though they are both valid.
  It is not ok to use spaces in >> or 2> or 2>&1 or 1>&2 (before or after is ok).
• In Windows NT 4, early Windows 2000 versions, and OS/2 there used to be some ambiguity with ECHOed lines ending with a 1 or 2, immediately followed by a >:
  ECHO Hello world2>file.txt would result in an empty file file.txt and the text Hello world (without the trailing «2») on screen (CMD.EXE would interpret it as ECHO Hello world 2>file.txt).
  In Windows XP the result is no text on screen and file.txt containing the line Hello world2, including the trailing «2» (CMD.EXE interprets it as ECHO Hello world2 >file.txt).
  To prevent this ambiguity, either use parentheses or insert an extra space yourself:
  ECHO Hello World2 >file.txt
(ECHO Hello World2)>file.txt
• «Merging» Standard Output and Standard Error with 2>&1 can also be used to pipe a command’s output to another command’s Standard Input:
  somecommand 2>&1 | someothercommand

• Redirection overview page
• Use the TEE command to display on screen and simultaneously redirect to file

How-to: Redirection

command > filename command >&n	Redirect command output to a file Redirect command output to the input of handle n
command >> filename	APPEND into a file
command < filename command <&n	Type a text file and pass the text to command. Read input from handle n and write it to command.
commandA | commandB	Pipe the output from commandA into commandB
commandA & commandB	Run commandA and then run commandB
commandA && commandB	Run commandA, if it succeeds then run commandB
commandA || commandB	Run commandA, if it fails then run commandB
commandA && commandB || commandC If commandA succeeds run commandB, if commandA fails run commandC If commandB fails, that will also trigger running commandC.

Success and failure are based on the Exit Code of the command.
In most cases the Exit Code is the same as the ErrorLevel

For clarity the syntax on this page has spaces before and after the redirection operators, in practice you may want to omit those to avoid additional space characters being added to the output. Echo Demo Text> Demofile.txt

Numeric handles:

STDIN  = 0  Keyboard input
STDOUT = 1  Text output
STDERR = 2  Error text output
UNDEFINED = 3-9 (In PowerShell 3.0+ these are defined)

When redirection is performed without specifying a numeric handle, the the default < redirection input operator is zero (0) and the default > redirection output operator is one (1). This means that ‘>‘ alone will not redirect error messages.

   command 2> filename       Redirect any error message into a file
   command 2>> filename      Append any error message into a file
  (command)2> filename       Redirect any CMD.exe error into a file
   command > file 2>&1       Redirect errors and output to one file
   command > fileA 2> fileB  Redirect output and errors to separate files

   command 2>&1 >filename    This will fail!

Redirect to NUL (hide errors)

   command 2> nul            Redirect error messages to NUL
   command >nul 2>&1         Redirect error and output to NUL
   command >filename 2> nul  Redirect output to file but suppress error
  (command)>filename 2> nul  Redirect output to file but suppress CMD.exe errors

Any long filenames must be surrounded in «double quotes».
A CMD error is an error raised by the command processor itself rather than the program/command.

To prevent the > and < characters from causing redirection, escape with a caret: ^> or ^<

Redirection — issues with trailing numbers

Redirecting a string (or variable containing a string) will fail to work properly if there is a single numeral at the end, anything from 0 to 9.
e.g. this will fail:
Set _demo=abc 5
Echo %_demo%>>demofile.txt

One workaround for this is to add a space before the ‘>>’ but that space will end up in the output.
Moving the redirection operator to the front of the line completely avoids this issue, but is undocumented syntax.:

Set _demo=abc 5
>>demofile.txt Echo %_demo%

Create a new file

Create an empty file using the NUL device:

Type NUL >EmptyFile.txt
or
Copy NUL EmptyFile.txt
or
BREAK > EmptyFile.txt

Multiple commands on one line

In a batch file the default behaviour is to read and expand variables one line at a time, if you use & to run multiple commands on a single line, then any variable changes will not be visible until execution moves to the next line. For example:

 SET /P _cost=»Enter the price: » & ECHO %_cost%

This behaviour can be changed using SETLOCAL EnableDelayedExpansion

Redirect multiple lines

Redirect multiple lines by bracketing a set of commands:

(
  Echo sample text1
  Echo sample text2
) > c:\logfile.txt

Unicode

The CMD Shell can redirect ASCII/ANSI (the default) or Unicode (UCS-2 le) but not UTF-8.
This can be selected by launching CMD /A or CMD /U

In Windows 7 and earlier versions of Windows, the redirection operator ‘>’ would strip many Extended ASCII /Unicode characters from the output.
Windows 10 no longer does this.

Pipes and CMD.exe

You can redirect and execute a batch file into CMD.exe with:

CMD < sample.cmd

Surprisingly this will work with any file extension (.txt .xls etc) if the file contains text then CMD will attempt to execute it. No sanity checking is performed.

When a command is piped into any external command/utility ( command | command ) this will instantiate a new CMD.exe instance.
e.g.
TYPE test.txt | FIND «Smith»

Is in effect running:

TYPE test.txt | cmd.exe /S /D /C FIND «Smith»

This has a couple of side effects:
If the items being piped (the left hand side of the pipe) include any caret escape characters ^ they will need to be doubled up so that they survive into the new CMD shell.
Any newline (CR/LF) characters in the first command will be turned into & operators. (see StackOverflow)

On modern hardware, starting a new CMD shell has no noticable effect on performance.

For example, this syntax works, but would fail if the second or subsequent (piped) lines were indented with a space:
@Echo Off
Echo abc def |^
Find «abc» |^
Find «def»> outfile.txt

Multi-line single commands with lots of parameters, can be indented as in this example:

Echo abc def ^
  ghi jkl ^

  mno pqr

Redirection anywhere on the line

Although the redirection operator traditionally appears at the end of a command line, there is no requirement that it do so.
All of these commands are equivalent:

Echo A B>C
Echo A>C B
Echo>C A B
>C Echo A B

All of them Echo «A B» to the file «C».

If the command involves a pipe such as DIR /b | SORT /r then you will still want to put the redirection at the end so that it captures the result of the SORT, but there are some advantages to putting the redirection at the start of the line.

Code like this:

Set _message=Meet at 2
Echo %_message%>schedule.txt

Will inadvertently interpret the “2” as part of the redirection operator.

One solution is to insert a space:

Echo %_message% >schedule.txt 

This assumes that the space won’t cause a problem. If you’re in a case where that space will indeed cause a problem, you can use the trick above to move the redirection operator to a location where it won’t cause any trouble:

>schedule.txt Echo %_message%  

Example via Raymond Chen

The idea of redirection anywhere in the line was first introduced in version 2 of sh, written by Ken Thompson in 1972.

Exit Codes

If the filename or command is not found then redirection will set an Exit Code of 1

When redirecting the output of DIR to a file, you may notice that the output file (if in the same folder) will be listed with a size of 0 bytes. The command interpreter first creates the empty destination file, then runs the DIR command and finally saves the redirected text into the file.

The maximum number of consecutive pipes is 2042

Examples

   DIR >MyFileListing.txt
   
   DIR /o:n >"Another list of Files.txt"

   DIR C:\ >List_of_C.txt 2>errorlog.txt

   DIR C:\ >List_of_C.txt & DIR D:\ >List_of_D.txt

   ECHO y| DEL *.txt

   ECHO Some text ^<html tag^> more text

   COPY nul empty.txt

   MEM /C >>MemLog.txt

   Date /T >>MemLog.txt

   SORT < MyTextFile.txt

   SET _output=%_missing% 2>nul
   
   FIND /i "Jones" < names.txt >logfile.txt

   (TYPE logfile.txt >> newfile.txt) 2>nul

“Stupidity, outrage, vanity, cruelty, iniquity, bad faith, falsehood,
we fail to see the whole array when it is facing in the same direction as we” ~ Jean Rostand (French Historian)

Related commands

CON — Console device.
conIN$ and conOUT$ behave like stdin and stdout, or 0 and 1 streams but only with internal commands.
SORT — Sort input.
CMD Syntax
TYPE — Display the contents of one or more text files.
Command Redirection — Microsoft Help page (archived)
Successive redirections explained (1>&3 ) — Stack Overflow.
Equivalent PowerShell: Redirection — Spooling output to a file, piping input.
Equivalent bash command (Linux): Redirection — Spooling output to a file, piping input.

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