/dev/null discards unwanted output

All data written on a /dev/null or /dev/zero special file is discarded by the system. Use /dev/null to send any unwanted output from program/command and syntax is:

command >/dev/null

This syntax redirects the command standard output messages to /dev/null where it is ignored by the shell. OR

command 2>/dev/null

This syntax redirects the command error output messages to /dev/null where it is ignored by the shell. OR

command &>/dev/null

This syntax redirects both standard output and error output messages to /dev/null where it is ignored by the shell.

Example

Try searching user vivek in /etc/passwd file:

grep vivek /etc/passwd && echo "Vivek found" || "Vivek not found"

Sample outputs:

vivek:x:1000:1000:Vivek Gite,,,,:/home/vivek:/bin/bash
Vivek found

To ignore actual output and just display the message, modify your command as follows:

grep vivek /etc/passwd >/dev/null && echo "Vivek found" || "Vivek not found"

Sample outputs:

Vivek found

Consider the following example from the exit status chapter. The output of grep "^$username" $PASSWD_FILE > /dev/null is send to /dev/null where it is ignored by the shell.

#!/bin/bash
# set var 
PASSWD_FILE=/etc/passwd
 
# get user name
read -p "Enter a user name : " username
 
# try to locate username in in /etc/passwd 
# 
grep "^$username" $PASSWD_FILE > /dev/null
 
# store exit status of grep
# if found grep will return 0 exit stauts
# if not found, grep will return a nonzero exit stauts
status=$?
 
if test $status -eq 0
then
	echo "User '$username' found in $PASSWD_FILE file."
else
	echo "User '$username' not found in $PASSWD_FILE file."
fi