what does > nul 2>&1 mean in a batch statment

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

Answer 1

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.