The Command Block is a block that was introduced in 12w32a and was officially released in Minecraft 1.4.2. It was introduced as a way to help support Adventure Mode, SMP automation, and custom maps.
To find out more in detail, visit the Command Block page.
Singleplayer applications (SSP)
Command blocks can be used in single player to change the difficulty, change the state of the weather, or give you predesignated items. They are particularly useful for the /weather and /time set x commands, as they are only available in cheat mode otherwise. The /time set x command is especially useful, as it allows one to change the current time to a preset time at the press of a button. command blocks can also be used to make text appear in the persons chat menu. To do this, dig 2 blocks down in the ground, place a command block at the bottom of the hole, type this into the command block: tell @p <message> or tell <username> <message> then place a block on top and place a pressure plate on that block. If you typed @p when someone steps on it whoever stepped on it will get a message but not anybody else. if you typed in <username> when you or any other person steps on it whoever the username is will be sent the message: @ whispers to you: <message> in that form of text.You can also type: tell <your username> @p and whenever someone walks over it it will say: ''@ whispers to you: <username of whoever stepped on it>. If a mob steps on the pressure plate it will say the username of the closest person to the command block.
Elevator
You can also make an elevator using /tp ~0~y~0, where y is the vertical difference between the upper and lower elevator entrances. The elevator can also be made to tp a player to any x y z coordinate just by leaving out the ~ before the numbers. When ~ is left in the command, the normal x y z is set to 0 0 0 where the command was made, such as standing on a pressure plate or wherever the player is standing when the command block received power. If a pressure plate was at the x y z coordinates of -36 96 -12 that ran to a command block with a command of /tp @p ~3 ~4 ~5 it would tp the player to the coordinates of -33 100 -7. The same outcome can be achieved by having the command of /tp @p -34 100 -8 one block must be subtracted from the x and z axis to get to the right coordinates.
Eternal Day
By using Cobweb and a minecart, you can skip nights using /time set 0. A minecart takes 31 seconds to fall through a cobweb. Therefore, by using 23 stacked cobweb with a Detector Rail and several Powered Rail will keep the sun in the sky.
Alternatively you can use a item de-spawning on a wooden pressure pad. The item de-spawns off of the pad every 5 mins, at this time it triggers a command block reset of the time to 0, also it triggers a dispenser to drop a new item on the wooden pad. 5 Mins is the day cycle and will trigger before mobs spawn. This method however is limited to 64x9 = 576 cycles = 48 IRL hours of gameplay with that chunk loaded. In the snapshot 13w01a and higher, hoppers are added into the game that can pick up items and deposit them into blocks with an inventory. A mob grinder can keep the dispenser full with gunpowder, arrows, and zombie flesh.
Both of these methods require the chunk to be loaded to allow the system to work.
Alternatively, you could connect the command block to a repeating redstone pulse, such as a five-clock, or a daylight sensor as seen on the right. To prevent this filling up the chat box, set the gamerule "commandBlockOutput" to false using the command /gamerule commandBlockOutput false.
Starting in snapshot 13w01a, it is possible to use the new Daylight Sensor block as a more direct approach.
Adventure Map Making
If one wishes to create a Single Player adventure map, do /publish to allow all other commands (see below) to be used.
Multiplayer applications (SMP)
This section details the applications of the Command Block in multiplayer.
- Teleportation/Transport
Through /tp, one can create teleporters for public use on a server. Can be applied to a range of scenarios. For example, one could make a system of portals in a particularly large world in which all portals link to a central hub, which contains portals to all other portal locations creating a sort of "Fast Travel Hub"
- "Stop-Motion Animation"
By using /tp and MCEdit, one can copy a landscape, paste it in a faraway location, and change a few blocks. Wire a pressure plate or tripwire at each site, so that after a short delay to admire the scenery, the player is teleported using the /tp command in the command blocks. If a large amount of these copied and altered locations are wired so that the player teleports to them in sequence with a slight delay in between each, then this creates the illusion that the scenery around the player is moving, similarly to the techniques used in stop-motion animation.
- Lottery
Through /give @r, one can create a lottery. Keep in mind that now, /give will directly put items into one's inventory, instead of throwing them on the ground in front of the character.
- Jails
By rigging a clock to a command block and using /tp a whole bunch, you can force a player to stay at a certain place. If you do this it would be advisable to either turn off commands in your chat settings or do /gamerule commandBlockOutput false. Using the "Range" and "Minimum Range" parameters, you can have it teleport players back only when they're a certain distance away.
- Admin Only
By using the parameter [m=1], only players in Creative will be affected by the command block.
Hopefully only ops are in Creative on your server.
- Announcements
By using /me in a command block one can create announcements that could play even when the admin/owner wasn't there.
- Security Scan
By using /clear, you can scan people for items. If you want to remove certain items, use /clear @a(or <playername>) <itemid>. For example, on a server that doesn't want griefing you could have a clock connected to a command block set to /clear @a 259.
- Race Referee
Using /say @p, the command block can report the nearest player. If the command block is placed after a finish line, it will say the finishers in order.
- Creative Area/World Guard
Creating a "Creative Only" zone is possible through command blocks, but it is complex and more of a case-by-case basis. The basic idea would be to create a "fence" of command block affected zones so that, once a player flies in creative through it, they would be changed to survival or adventure mode.
A "World Guard" zone would be a lot simpler, just have a command block do /gamemode 2 @a[x y z r m] and when people leave, just have a button to change them to survival.
- Improving PvP without Plug-Ins
You can use /gamerule keepInventory true so players cannot steal each others items. Also, using /spawnpoint [x y z] and /tp [x y z] to help move players around while in PvP competitions.
- Starter Kits
You can easily give people a starter kit with a button without plug-ins: "/give @p[r=2] 274".
To prevent people pressing the button a second time and again getting their kit you can make two command blocks activated in order: 1. "/give @p[r=2 m=2] 274" 2."/gamemode 0 @p[r=2]"
- Special Colourful Words
Although you are not directly able to obtain colored/bold/italic text when typing into the Command Block GUI, through McEdit filters you can edit the text to have those properties just like how plug-ins change chat text properties on servers.
SethBling's McEdit Filter: ColourCommandBlockText
- Alarm System
When a player walks over a pressure plate, it can trigger a command block with /say @p
- Remove Players
Using coordinate and maximum parameters you can teleport everyone within a specific area to another specific area.
- Reward Room
If a certain player has been very nice,regular,or helpful to the sever but not quite meeting the requirements to be promoted to an admin, you could have a room full of buttons connected to Command Blocks with helpful effects, like giving the helpful player a stack of diamonds or a bedrock block, then have it connected to another command block, sending them to the spawn point. (It is VERY important this room is reinforced with bedrock, hidden, and you can only get in by teleporting to its co-ordinates to avoid abuse).
- Weather Machine
(Command: /toggledownfall and /weather thunder (to start or stop a thunderstorm)) Assuming only admins can get to it, a weather machine can be quite useful, you can turn rain on and off at will. One of the more helpful uses of this technique would be to use a combination of villagers and some form of redstone machinery to create and automatic rain disabler, this would allow you to shut off the rain almost immediately without needing to use the command, or to have an admin present. It can also be used to create, and/or end, a scenario where it is more advantageous to have rain as opposed to sunlight, and vice versa; such as during a forest fire, or when a thunderstorm is spawning monsters.
- Obstacle Course prizes
with tp @p and give @p, you could make an obstacle course or maze that when finished will give a player a prize, and will teleport them back to spawn or some other area.
- Time Machine
By making to similar places on one map,you can have a button activate a command block to tp you from one to another. This can be used to look like teleportation!
Application in custom maps
This section details the applications of the Command Block in custom maps.
One map that takes advantage of a lot of the features of the Command Block is SethBling's TF2 Map "Dustbowl" in Minecraft.
http://www.youtube.com/watch?v=_f2brU8hBWc&feature=plcp
Another example is the Hypixel's Gladiator Arena in which the fighting system is almost only based on the Command Block.
- Silent Command Block
Sometimes it's important in a map to keep the command blocks silent, may it be to keep the magic of the suddenly appearing items in the inventory, or because the channel telling that the player was teleported, it can break the mood of a map. To keep them silent (except when you ask them to speak), just use the /gamerule commandBlockOutput false.
- Safe Haven/Arena Fight Zone
Using pressure plates or tripwire, make areas (like a castle for instance) a different difficulty (for this instance I will use peaceful). the doors could have tripwire hooked to a command block that changes ones difficulty to peaceful, creating a sort of "Safe Haven". one could also do it the other way around, creating a more dangerous zone, such as arenas having the difficulty of hard, rather than normal or easy.
- Detecting Cheaters
Using parameter [m=1] , you can affect those who are in Creative, or survival with parameter [m=0].
- It's bigger on the inside
This is a simple one, just have a system of tp-ing command blocks at the entrance/exit of a place, and you can build the interior somewhere else, allowing you to cheat space restriction. (example of use: you want interior walls to be wool, but exterior walls to be wood (normally 2m thick walls).
You can make the outside of the house be 8x10 m, and the inside of the house be 8x10 m.) Or, have the inside of the house 20x20m instead!
- Save game
By using the "/spawnpoint" command, one can easily make a button-activated checkpoint.
- Lava parkours
As said before, there is a command that makes the player able to keep his inventory upon death: /gamerule keepInventory true. Simply connect this to a pressure pad before a parkour level over lava and you don't have to use any kind of chest minecart (especially useful when the player has it's full inventory, which is bigger than a single chest).
- Still want a bed?
It is true that the /spawnpoint command is really useful because you don't have to wait for the night to create a checkpoint, but what if you want to have a BUD switch connected to the bed or something of the sort? Then, you just need to have a pressure plate (it's more discreet) connected to a block with the /time set 18000 command, and it will set the time to night so the player can sleep.
- Time and weather following the scenario
Let's say your map starts on a cold stormy night and when the player starts, for some random reason, there's a bright sun outside! Or what if you want to start on a bright day and the rain decides to join along? Fear not, for there is a weather command. Just use the /weather input command with, as input, clear, rain or thunder. Along with this, you can also use /time set input with as input a number: 0 is sunrise, 6000 is noon, 12000 is dusk and 18000 is midnight.
- Detecting dirty cheaters who switched to Peaceful
Create a hostile mob (so it disappears when switching to Peaceful) that never despawns if the player is far away (use third-party software to do so) and place it on a pressure plate. Make sure it will keep it pressed infinitely, so make sure it can't jump or walk away. Make a redstone circuit that causes a command block to activate when input from pressure plate ceases to exist. Place a message inside the block that informs the player on chat that the map has been broken and must be redownloaded. This way, switching to Peaceful will cause the mob to vanish and activate the message. You can even make a teleportation command block so that a cheater is banished from the map to a small room without a way out as soon as he switches to Peaceful.
- Talking Adventure Map(featuring an easy Quest System!)
The /say command is really useful because it makes a text appear into the chat. It's maybe one of the greatest use of the Command Block as you don't need silly signs or long books to show the game rules. Just put a bunch of command blocks in lines with repeaters set to two or three ticks (so the player isn't spammed) and you can easily remove a chest of books or a lot of signs.
Another use of the command is talking NPCs and other mobs. Imagine you enter a butchery and you want the butcher to say something. Before, you needed to use signs or books, using some room in a butchery and putting objects that sometimes seemed random, but now... You just have to use the /say command and the butcher will talk. Maybe a pig behind the counter will even beg for mercy! Let's take another example: you are in a factory and an alarm suddenly rings and says that it's going to explode. Having it in the chat, especially if the text is long, keeps the stressfull mood; the same thing works for bomb timers. The player will get more into the map's mood if the chat displays '10...' '9...' '8...' also.
Last but not least, it makes it easier to create a Quest System. Let's say the player gets in a butchery. He activates through a pressure plate connected to a RS NOR Latch (so it can't be activated twice) and a command block with the /say command in which the butcher asks for the player's help: he need to kill a pig (shame on him). The player gets to the pig that is standing on a stone pressure plate, that turns off when the pig is dead. So, when the player gets back to the butchery, he activates another circuit containing yet another RS NOR Latch and two command blocks with two commands. First, the /say command in which the butcher thanks the player, and other one, the /give command, so the player gets the reward. Along with that, don't forget to use the @p command so the butcher says the player's name. For example, if the command block is set to do this: /say Thanks, @p. You helped me a lot killing that pig., the channel will say: "@]: Thanks, <name of the player>. You helped me a lot killing that pig." This makes the map way cooler and looks like it's made for the player as it says his/her name!
- Making a Store
By using /give @p[lm=(level)] (item) (amount) and /xp -(level)l @p[lm=(level)] you can make a shop system that trades a certain amount of exp for items. For instance, if you made a command block with /give @p[lm=5] 2 64 and another with /xp -5l @p[lm=5] connected to the same redstone current, it will take 5 levels from the player, and in return, give them 64 grass blocks.
- Making a Store using xp as a currency currently does not work as you can not give negative xp to a player. however you can set one block to
/clear @p (item) to "trade" items. use with caution as this will get rid of all instances of item in players inventory.
See also
- Command Block
- Multiplayer
- Adventure Mode