[bash] How to hide command output in Bash

I want to make my Bash scripts more elegant for the end user. How do I hide the output when Bash is executing commands?

For example, when Bash executes

yum install nano

The following will show up to the user who executed the Bash:

Loaded plugins: fastestmirror
base                                                     | 3.7 kB     00:00
base/primary_db                                          | 4.4 MB     00:03
extras                                                   | 3.4 kB     00:00
extras/primary_db                                        |  18 kB     00:00
updates                                                  | 3.4 kB     00:00
updates/primary_db                                       | 3.8 MB     00:02
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package nano.x86_64 0:2.0.9-7.el6 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
 Package         Arch              Version                Repository       Size
================================================================================
Installing:
 nano            x86_64            2.0.9-7.el6            base            436 k

Transaction Summary
================================================================================
Install       1 Package(s)

Total download size: 436 k
Installed size: 1.5 M
Downloading Packages:
nano-2.0.9-7.el6.x86_64.rpm                              | 436 kB     00:00
warning: rpmts_HdrFromFdno: Header V3 RSA/SHA256 Signature, key ID c105b9de: NOKEY
Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
Importing GPG key 0xC105B9DE:
 Userid : CentOS-6 Key (CentOS 6 Official Signing Key) <[email protected]>
 Package: centos-release-6-4.el6.centos.10.x86_64 (@anaconda-CentOS-201303020151.x86_64/6.4)
 From   : /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing : nano-2.0.9-7.el6.x86_64                                      1/1
  Verifying  : nano-2.0.9-7.el6.x86_64                                      1/1

Installed:
  nano.x86_64 0:2.0.9-7.el6

Complete!

Now I want to hide this from the user and instead show:

    Installing nano ......

How can I accomplish this task? I will definitely help to make the script more user friendly. In case an error occurs then it should be shown to the user.

I would like to know how to show same message while a set of commands are being executed.

This question is related to bash shell

The answer is


You should not use bash in this case to get rid of the output. Yum does have an option -q which suppresses the output.

You'll most certainly also want to use -y

echo "Installing nano..."
yum -y -q install nano

To see all the options for yum, use man yum.


A process normally has two outputs to screen: stdout (standard out), and stderr (standard error).

Normally informational messages go to sdout, and errors and alerts go to stderr.

You can turn off stdout for a command by doing

MyCommand >/dev/null

and turn off stderr by doing:

MyCommand 2>/dev/null

If you want both off, you can do:

MyCommand 2>&1 >/dev/null

The 2>&1 says send stderr to the same place as stdout.


You can redirect stdout to /dev/null.

yum install nano > /dev/null

Or you can redirect both stdout and stderr,

yum install nano &> /dev/null.

But if the program has a quiet option, that's even better.


>/dev/null 2>&1 will mute both stdout and stderr

yum install nano >/dev/null 2>&1

.SILENT:

Type " .SILENT: " in the beginning of your script without colons.


You can redirect the output to /dev/null. For more info regarding /dev/null read this link.

You can hide the output of a comand in the following ways :

echo -n "Installing nano ......"; yum install nano > /dev/null; echo " done."; 

Redirect the standard output to /dev/null, but not the standard error. This will show the errors occurring during the installation, for example if yum cannot find a package.

echo -n "Installing nano ......"; yum install nano &> /dev/null; echo " done.";

While this code will not show anything in the terminal since both standard error and standard output are redirected and thus nullified to /dev/null.