/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:
The last syntax redirects the the command error to /dev/null where it is ignored by the shell.
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