How do I install a Left 4 Dead 2 server on debian?

First of all install steam, or the Half Life Dedicated Server (a.k.a. hldsupdatetool, see This site)

wget http://www.steampowered.com/download/hldsupdatetool.bin

Install it ./hldsupdatetool.bin after chmod +x if necessary. It will put steam in the current directory.

Check the tool is at the last version with ./steam (multiple times if necessary, until it displays the help message).

Then the install a game just do well with

./steam -command update -game "left4dead2" -dir .

(It will install l4d2 in the current directory, creating left4dead2/ subdir.)

Hint: the game names can be changed to another game. See the list with ./steam -command list

Bonus: run your server in screen (within the good directory)

#!/bin/bash
screen -d -m -S l4d2-server ./srcds_run -console -game left4dead2 -log on -hostip 88.xxx.x.x -hostport 27016 -clientport 27006 -nohltv +exec server.cfg +map c5m1_waterfront -autoupdate