Print on terminal and into file simultaneously?

Question

I have a shell script that greps some data.. I want to print the result into a file, but doing that prevents the result being displayed on the terminal. Is there a way that

Answer 1

Note you can add the -a flag to tee to append to the output file

[me@home]$ echo hello | tee out.txt
hello
[me@home]$ echo hello again | tee -a out.txt
hello again
[me@home]$ cat out.txt
hello
hello again