command_1 `command_2 -options`
Backquote key: The back-quote key is usually located at the same place as the tilde, above the [Tab] key.
This will execute “command_2” and it's output will become the input to “command_1”.
You can of course use pipes to do the same thing, if you don't know what a pipe is, please see the Section called Usage. For example instead of doing:
less $cat file1.txt file2.txt
You could do:
cat file1.txt file2.txt | less