Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have the following command:

find / -name libGL.so.1

Which returns lots of lines with "Permission denied". I want to exclude such lines, so I added the following:

find / -name libGL.so.1 | grep -v 'denied'

But the output is the same - my grep -v 'denied' is not filtering out the lines with Permission denied. I've tried many variations, looked over grep tutorials, but I cannot figure out the problem. Any suggestions?

share|improve this question
up vote 24 down vote accepted

That's nothing to do with grep - it's because the pipe | redirects the standard output stream stdout whereas the Permission denied messages are in the standard error stream stderr. You could achieve the result you want by combining the streams using 2>&1 (redirect the stream whose file descriptor is 2 to the stream whose file descriptor is 1) so that stderr as well as stdout gets piped to the input of the grep command

find / -name libGL.so.1 2>&1 | grep -v 'denied'

but it would be more usual to simply discard stderr altogether by redirecting it to /dev/null

find / -name libGL.so.1 2>/dev/null

Using |& instead of 2>&1 |

If you take a look at the Bash man page you'll likely notice this blurb:

If |& is used, the standard error of command is connected to command2's standard input through the pipe; it is shorthand for 2>&1 |.

So you can also use this construct as well if you want to join STDERR and STDOUT:

find / -name libGL.so.1 |& grep -v 'denied'
share|improve this answer
Additional note on combining them: If for some bizarre reason the file exists at /foo/bar/denied/libGL.so.1, combining stdout and stderr then filtering would hide the result – Izkata May 12 '14 at 18:17

Your command should be:

find / -name libGL.so.1 2>/dev/null

Find is complaining about permissions on standard error (fd2). In order to eliminate those lines, redirect (>) standard out to the bit bucket (/dev/null).

share|improve this answer

The "permission denied" lines are going to the stderr (standard error) stream, but you are piping stdout (standard out) through grep.

You can redirect away stderr entirely with

find / -name libGL.so.1 2> /dev/null
share|improve this answer

Have you tried calling the command with sudo?

sudo find / -name libGL.so.1

If it still shows the message, use the already mentioned redirect of stderr (fd=2) to nirvana (/dev/null):

sudo find / -name libGL.so.1 2> /dev/null

More ideas here, good luck!

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.