In Linux, there are two special files /dev/null and /dev/tty. /dev/null will drop all the data written to it, i.e, when program writes data to this file, it means the program has completed the data write operation. But in  fact it does nothing, if you just want the status of a command but not the output of a command, this feature will be very useful. See below shell codes:    /> vi test_dev_null.sh        #!/bin/bash    if grep hello TestFile > /dev/null    then        echo "Foun...