/dev/null discards unwanted output

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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: <syntaxhighlight lang="bash" >grep vivek /etc/passwd && echo "Vivek found" || "Vivek not found"</source> 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: <syntaxhighlight lang="bash" >grep vivek /etc/passwd >/dev/null && echo "Vivek found" || "Vivek not found"</source> 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. <syntaxhighlight lang="bash" >#!/bin/bash

  1. set var

PASSWD_FILE=/etc/passwd

  1. get user name

read -p "Enter a user name : " username

  1. try to locate username in in /etc/passwd

grep "^$username" $PASSWD_FILE > /dev/null

  1. store exit status of grep
  2. if found grep will return 0 exit stauts
  3. 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</source> ← Empty file creationHomehere documents →