What does > nul 2>&1 mean in a batch statement

Question

I currently have a batch statement that looks like this

findstr "PreprocessorDefinitions=.*%D_KEYWORD%" %PROJ% > nul 2>&1
if errorlevel 1 (
    set D_OPT=
) else (
    set D_OPT=/D%D_KEYWORD%
)

I wanted to know what the following means ?

> nul 2>&1

I looked here and it states that

... >nul 2>nul

means ignore output of command and ignore error messages

Now my question is how can I modify this command

 findstr "PreprocessorDefinitions=.*%D_KEYWORD%" %PROJ% > nul 2>&1

to show everything and not to ignore the error messages

Standard output is going to `nul` and standard error output (file descriptor 2) is being sent to standard output (file descriptor 1) so both error and normal output go to the same place. In Windows, `nul` is a null device, which means the output is just flushed and you don't see it. Thus, in this case, all output is being flushed. — lurker, Jun 13 '15 at 00:35
If you want to see everything on your screen, just get rid of the `> nul 2>&1`. — lurker, Jun 13 '15 at 00:35
Possible duplicate of [In the shell, what does " 2>&1 " mean?](https://stackoverflow.com/questions/818255/in-the-shell-what-does-21-mean) — wesinat0r, Dec 08 '18 at 19:58

score 62 · Accepted Answer · edited Aug 12 '21 at 08:43

62

Don't use a redirection operator, which is what ">" is.

All programs have three streams:

Standard Input (the input from the console)
Standard Output (general logging/UI output to the console)
Standard Error (logging/UI output to the console meant for error messages or other exceptional behavior)

command >nul

^ This says to pipe the standard-output stream to null.

command 2>nul

^ This says to pipe the standard-error stream to null.

command 2>&1

^ This says to pipe the standard-error stream to the same place as the standard-output stream.

edited Aug 12 '21 at 08:43

Chris D

answered Jun 13 '15 at 00:36

iAdjunct

19

you say don't use it, but you did not explain why – MushyPeas Oct 08 '19 at 21:07
7

">" is actually a redirection operator; "|" is the piping operator. – galaxis May 10 '20 at 15:40
@MushyPeas Agree. Very confusing. – Idanref Aug 28 '22 at 13:12
@MushyPeas, This is a direct answer to the OP's question. e.g. How do I see the output? Answer: Don't use the redirection operator. Could be worded better, but it is understandable. – Peter Lieber Jan 11 '23 at 18:32

1 Answers1