Reputation: 6132

How can I suppress all output from a command using Bash?

I have a Bash script that runs a program with parameters. That program outputs some status (doing this, doing that...). There isn't any option for this program to be quiet. How can I prevent the script from displaying anything?

I am looking for something like Windows' "echo off".

Upvotes: 408

Answers (11)

Dan J.

Reputation: 131

I know this question is 15 years old, but it's the top result for searches for preventing output from a script, and there is (to my mind, at least) no valid answer given. The question specifically asks for something similar to the Windows "echo off" command. "echo off" is a command that is (or at least was, in the old cmd.com days) often put at the top of the script. It's a way to silence the script FROM WITHIN THE SCRIPT itself. All of the answer here seem to be addressing silencing the script from the command line when you run it, or silencing the output of specific lines within the script. I was looking for a way to silence all output from the script from within the script, and that's not found here.

The answer I found was to put this at the top of the script:

exec > /dev/null 2>&1

and at the bottom:

exec &>/dev/tty

Obviously, this prevents any errors from being seen and isn't appropriate for all use cases. If the script fails before restoring output in a session, you would see no output until you manually restored it.

Upvotes: 2

Violet Giraffe

Reputation: 33605

If you're running a command in the background and want to suppress its output, the syntax is the following:

(my_command > /dev/null &)
or
(my_command > /dev/null 2>&1 &)

Upvotes: 2

Brian White

Reputation: 457

>&- closes the filedescriptor without even redirecting to /dev/null

foo 2>&- >&-

Can close stdin too foo 2>&- >&- <&-

Upvotes: 4

Lucas Gabriel Sánchez

Reputation: 41670

Like andynormancx' post, use this (if you're working in an Unix environment):

scriptname > /dev/null

Or you can use this (if you're working in a Windows environment):

scriptname > nul

Upvotes: 8

andynormancx

Reputation: 13762

The following sends standard output to the null device (bit bucket).

scriptname >/dev/null

And if you also want error messages to be sent there, use one of (the first may not work in all shells):

scriptname &>/dev/null
scriptname >/dev/null 2>&1
scriptname >/dev/null 2>/dev/null

And, if you want to record the messages, but not see them, replace /dev/null with an actual file, such as:

scriptname &>scriptname.out

For completeness, under Windows cmd.exe (where "nul" is the equivalent of "/dev/null"), it is:

scriptname >nul 2>nul

Upvotes: 680

Rohan Dsouza

Reputation: 101

In your script you can add the following to the lines that you know are going to give an output:

some_code 2>>/dev/null

Or else you can also try

some_code >>/dev/null

Upvotes: 1

semente

Reputation: 7523

An alternative that may fit in some situations is to assign the result of a command to a variable:

$ DUMMY=$( grep root /etc/passwd 2>&1 )
$ echo $?
0
$ DUMMY=$( grep r00t /etc/passwd 2>&1 )
$ echo $?
1

Since Bash and other POSIX commandline interpreters does not consider variable assignments as a command, the present command's return code is respected.

Note: assignement with the typeset or declare keyword is considered as a command, so the evaluated return code in case is the assignement itself and not the command executed in the sub-shell:

$ declare DUMMY=$( grep r00t /etc/passwd 2>&1 )
$ echo $?
0

Upvotes: 21

ivanleoncz

Reputation: 10065

Take a look at this example from The Linux Documentation Project:

3.6 Sample: stderr and stdout 2 file

This will place every output of a program to a file. This is suitable sometimes for cron entries, if you want a command to pass in absolute silence.
     rm -f $(find / -name core) &> /dev/null 

That said, you can use this simple redirection: