Cheat: Portal Gun Hack
This process modifies your game files, so make back-ups of the proper files and directories before attempting this hack.

You need both Portal and Half-life 2 for starters. Install or re-install both games now.

Back up your Portal directory. Unless you changed the install path, the directory is in
...Steamsteamapps(your_username)portal
. If you make a mistake during this hack, you may need to re-download Portal through Steam (or at worse, Half-life 2 through Steam).

Download and install GCFScape
if you do not have it already. This program allows you to access the cached game files for games using the Source engine.

Head into the directory ...Steamsteamapps
for all the available GCF archives available. Open the file half-life 2 content.gcf
via GCFScape. Click the hl2
folder on the left pane of the GCFScape Explorer window. Right mouse click maps
and select the command Extract
to place all the contents of the maps folder into the directory ...Steamsteamapps he_great_bundiniportalportal
. This merges Half-life 2 maps with the Portal map folder.

Repeat the above step with the scenes
folder via GCFScape.

Boot up Steam to run Portal. Drop the developer console with ‘~’ (you may need to enable it under your keyboard options or enable it via the -console
command switch on the executables shortcut).

On the developer console, type maps *
to list all the available maps; this should inclde the Half-life 2 maps imported from the previous steps. Type map
and then the name of that map (i.e., map d1_canals_01
).

Once the map is loaded and you can play, drop the console and enable the cheats for Portal by entering sv_cheats 1
. Give yourself all weapons (including the Portal Gun) by entering impulse 101
. You may need to input upgrade_portalgun
to enable you to fire both portals.

Enjoy the havoc. Note that this hack also works with Episode 1 and Episode 2. You will notice that while NPCs from Half-life cannot pass through portals, all other inert objects (including yourself) and weapons fire will pass through with no problems.