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

Answer 2

Does exactly your thing

http://linux.die.net/man/1/tee

Answer 3

Pipe your output to the tee command.

Example:

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

Note that the stdout of echo is printed out as well as written to the file specified by thr tee command.