How to read and write to standard output in linux

1.tee name

tee- read from standard input and write to standard output and files

2. tee synopsis

tee [OPTION]... [FILE]...
3. tee frequently used options
-a, --append
      append to the given files, do not overwrite
4. tee examples in linux

Standard output redirected to file as well as to terminal:

$ free | tee tee.txt
$ cat tee.txt

standard output redirected to file with tee

Source taken from http://linuxconfig.org/