Is there a /dev/null on Windows?

Question

What is the equivalent of /dev/null on Windows?

Answer 1

I think you want NUL, at least within a command prompt or batch files.

For example:

type c:\autoexec.bat > NUL

doesn't create a file.

(I believe the same is true if you try to create a file programmatically, but I haven't tried it.)

In PowerShell, you want $null:

echo 1 > $null

Answer 2

According to this message on the GCC mailing list, you can use the file "nul" instead of /dev/null:

#include <stdio.h>

int main ()
{
    FILE* outfile = fopen ("/dev/null", "w");
    if (outfile == NULL)
    {
        fputs ("could not open '/dev/null'", stderr);
    }
    outfile = fopen ("nul", "w");
    if (outfile == NULL)
    {
        fputs ("could not open 'nul'", stderr);
    }

    return 0;
}

(Credits to Danny for this code; copy-pasted from his message.)

You can also use this special "nul" file through redirection.

Answer 3

NUL in Windows seems to be actually a virtual path in any folder. Just like .., . in any filesystem.

Use any folder followed with NUL will work.

Example,

echo 1 > nul
echo 1 > c:\nul
echo 1 > c:\users\nul
echo 1 > c:\windows\nul

have the same effect as /dev/null on Linux.

This was tested on Windows 7, 64 bit.

Answer 4

Jon Skeet is correct. Here is the Nul Device Driver page in the Windows Embedded documentation (I have no idea why it's not somewhere else...).

Here is another:

• The null device in the registry
• Special file names
• More on file naming

Answer 5

NUL works programmatically as well. E.g. the following:

freopen("NUL", "w", stderr);

works as expected without creating a file. (MSVC++ 12.0)

Answer 6

If you need to perform in Microsoft Windows the equivalent of a symlink to /dev/null in Linux you would open and administrator's cmd and type:

For files:

mklink c:\path\to\file.ext NUL:

Or, for directories:

mklink /D c:\path\to\dir NUL:

This will keep the file/direcotry always at 0 byte, and still return success to every write attempt.

Answer 7

You have to use start and $NUL for this in Windows PowerShell:

Type in this command assuming mySum is the name of your application and 5 10 are command line arguments you are sending.

start .\mySum  5 10 > $NUL 2>&1

The start command will start a detached process, a similar effect to &. The /B option prevents start from opening a new terminal window if the program you are running is a console application. and NUL is Windows' equivalent of /dev/null. The 2>&1 at the end will redirect stderr to stdout, which will all go to NUL.

Answer 8

In Windows10, if you want to use NUL like a file e.g.

robocopy .\test NUL /move /minage:30 
# delete all files older than 30 days using robocopy

These answers all don't work.

You get the error:

ERROR 123 (0x0000007B) Accessing Destination Directory \\.\NUL\
The filename, directory name, or volume label syntax is incorrect.

However, it works if you do in cmd.exe:

echo 1 > NUL

So NUL doesn't behave exactly like a /dev/null file.

However, for the robocopy command, you can do something like:

robocopy .\test NUL\null /move /minage:30 

Then it works!

In Powershell, the $null works only as stdout redirection

echo 1 > $null

But you can't use $null in a command like for robocopy instead of a file. Neither does $null\null work.

So all I could find to have the same effect like cmd.exe in PowerShell, is to call cmd.exe from within PowerShell like this:

mkdir test1
cd test1
echo "" > test1.txt
echo "" > test2.txt
echo "" > test3.txt

$path = '.\test1'
cmd.exe /c "robocopy $path NUL\null /move"

# also this works:
cmd.exe /c "robocopy $path .\NUL\null /move"

So NUL doesn't behave exactly like /dev/null folder but like a folder which can have phantom files inside it when used as a target file except you use it with > redirection, then it behaves as it is like a null device/file.

In addition it is to be mentioned that cmd.exe creates a NUL when first used. But one cannot look into it.