How to suppress tar error messages in when piping

Here are couple of alternatives that involve redirecting STDERR of both tar and grep :

• Use bash command grouping {}:

  { tar -xvf file.tar.bz2 | grep "something" ;} 2>/dev/null
  

• Using a subshell () :

  ( tar -xvf file.tar.bz2 | grep "something" ) 2>/dev/null
  

Note that if you want to redirect STDERR of a single process its better to use Oli's answer instead.

On a different note, if you want to grep something over both the STDOUT and STDERR of tar use :

tar -xvf file.tar.bz2 |& grep "something"

This will also cause the STDERR of tar to be exhausted.

This is actually a shorthand for :

tar -xvf file.tar.bz2 2>&1 | grep "something"

The pipe forms a separate clause in the command so the redirection in...

tar -xvf file.tar.bz2 | grep "something" 2>/dev/null 

...is redirecting the STDERR from grep, not tar.

To fix, simply reorder things so your redirect is with your tar command:

tar -xvf file.tar.bz2 2>/dev/null | grep "something"