Enable Cheat mode, then press tilde [~] and enter "/god" at the console window.

Enable Cheat mode. Then press [~] and enter "/map name" at the console window, where name is one of the map names below.

Maps:

• Training
  Ofboot1
  Ofboot2
  Ofboot3
  Ofboot4

• Regular game
  Generally, single player maps have the following form:

  of<0-7>a<0-5>letter

  A few valid map map names are, "of0a0", "of1a4b" and "of6a4".

1. Load the game using this command line:

   hl.exe -dev -console -game gearbox
   or 
   SierraHalf-Lifehl.exe -console +sv_cheats 1 -game gearbox 

2. Press the tilde key [~] to activate cheat mode.

Enable Cheat mode. Then press [~] and enter "impulse 101" at the console window.

Enable Cheat mode. Then press [~] and enter "/noclip" at the console window.

Enable Cheat mode. Then press [~] and enter "give item" at the console window, where item is the object you wish to create. Example:

Give weapon_knife

Object list

• Ammunition Ammo_556
  Ammo_772

• Weapons Weapon_displacer
  Weapon_grapple
  Weapon_knife
  Weapon_pipewrench
  Weapon_eagle
  Weapon_M249
  Weapon_Shockrifle
  Weapon_Sniperrifle
  Weapon_SporeLauncher