do me a example for shell command exec usage

Sure, here's an example of using the shell command `exec` in a shell script:

#!/bin/bash

# Execute a command and redirect its output to a file
exec ls -l > /tmp/list.txt

# The following command will not be executed
echo "This will not be printed to the console"

In this example, the `exec` command is used to run the `ls -l` command and redirect its output to a file named `/tmp/list.txt`. After the `exec` command completes, the script will continue to execute any remaining commands in the script. However, in this case, the `echo` command will not be executed because the `exec` command replaces the current shell process with the `ls` command.