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