Using tee To Split CLI Output

Store the output of some CLI operation and see the results in real-time

tail -f /var/log/postgresql/postgresql-13-main.log | grep deadlock | tee ~/postgres-deadlocks.log

This command will stream the logs written to /var/log/postgresql/postgresql-13-main.log, filter for lines containing deadlock, writes those lines to ~/postgres-deadlocks.log, and finally display that output to the terminal.

Use tee --append to append to the specified file instead of the default of overwriting it.