echo
echo is a console command available in all 
GoldSrc, 
Source, and 
Source 2 games.
It is used to print text into the console window. When used in tandem with scripts, the echo command can prove to be very useful in cases where you will need to debug problems.
Syntax
echo <text>
Examples
echo Hello world
Special use
When appended to a key bound to a + statement (but only directly), the key code will be appended
bind shift “+duck; echo key :”
key : 79 will be seen in the console twice; once on press, once on release.
