tee [ options ] [ files ]
tee
options
files
Duplicate the standard input; send one copy to standard output and another copy to files .
Append output to files .
Ignore all interrupts.
Display a who listing on the screen, and store it in two files:
who | tee userlist ttylist
Display misspelled words, and add them to existing typos :
spell ch02 | tee -a typos