The `tee` utility copies standard input to standard output, making a copy in zero or more files. The output is unbuffered.
# Write the output both to the screen `STDOUT` and to the `filelist.txt`. $ ls | tee filelist.txt # The following command will take a backup of the crontab entries, and pass the # crontab entries as an input 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 – # By default tee command overwrites the file. You can instruct tee command # to append to the file using the option –a as shown below. $ ls | tee –a file # You can also write the output to multiple files as shown below. $ ls | tee file1 file2 file3 ## Reference: http://linux.101hacks.com/unix/tee-command-examples/