The Knife is a moderate weapon that allows the player to attack without a firearm and, in Grand Theft Auto: San Andreas, allows stealth kills that don't attract unwanted attention. It takes up the "melee" weapon slot.
In GTA San Andreas, some prostitutes wield the knife. It is used in many missions in the game like Madd Dogg's Rhymes, Amphibious Assault, The Da Nang Thang, Dam and Blast and Vertical Bird. The Knife is more than just a simple melee weapon. If CJ is aiming behind an opponent, he will execute a stealth kill, quietly slitting the victim's throat, useful when the player is trying to avoid detection and doesn't have a Silenced 9mm. The Knife only produces one wanted star when used to stealth kill a police officer.
The GTA IV rendition of the Knife resembles the knife used by Sylvester Stallone in the Rambo movies, and is similar in size and shape to the Buck-184 Buckmaster survival knife. Its shape greatly resembles that of the SOG Seal Pup as well. It can be purchased from Little Jacob for $100. Alternatively, it can be picked up from Eddie Low during his second encounter and from Dardan Petrela in the mission Bleed Out. Although silent kills like in GTA San Andreas are not in the game, 5 to 6 strikes with the knife will kill an opponent, and it will not warrant the player a wanted level. This can easily kill an enemy on single player or multiplayer because 4 to 6 quick taps of the Circle button on the Playstation 3 or the B button on Xbox 360 while locked on with this will either kill or critically injure anyone. Armor does not protect against knife attacks. The Knife can also be used for a one-hit kill counter-attack, by dodging an attack with the knife equipped, and pressing the attack button.
Some GTA IV players favor the Baseball Bat over the Knife due to higher damage, but the slower attack speed is a opening for the target to return attacks. With the Knife, its possible to kill a target without him being able to recover at all.
Tudor, Alderney - Can be found just off the northbound on-ramp to the Plumbers Skyway, near a decrepit building and some unused railroad tracks. Alternatively, a parking lot is also next to the location, with some scaffolding which the player can easily climb.
In GTA Vice City, the knife is bent and the tip is very stubby, resembling a Kukri.
In GTA San Andreas, the stealth kill has the same animation as the Hasty knife execution from Rockstar's Manhunt.
In GTA Liberty City Stories, the knife can perform a one-hit kill by hitting the target directly with the third stab.
In GTA IV, it is possible to knock a knife out of an opponent's hands with a baseball bat.