GNU/Linux tee command Write output from the middle of a pipe chain to a file and pass it back to the pipe
Example
You can also use tee command to store the output of a command in a file and redirect the same output to another command.
The following command will write current crontab entries to a file crontab-backup.txt and pass the crontab entries to sed command, which will do the substituion. After the substitution, it will be added as a new cron job.
$ crontab -l | tee crontab-backup.txt | sed 's/old/new/' | crontab –
