How do I change grass blocks within a set region to magma blocks? [duplicate]

Solution 1:

Use the fill command.

/fill x1 y1 z1 x2 y2 z2 magma 0 replace grass

When using the fill command, there is a limit of 32,768 blocks, so you will need to use multiple fill commands. If the fill volume is 1 block high, using the following coordinates in 9 commands should work (where y is the y-coordinate):

• -256 y -256 -76 y -76
• -256 y -75 -76 y 104
• -256 y 106 -76 y 256
• -75 y -256 105 y -76
• -75 y -75 105 y 104
• -75 y 106 105 y 256
• 106 y -256 256 y -76
• 106 y -75 256 y 104
• 106 y 106 256 y 256

If the fill volume is more than 1 block high, you will need to divide it into even more fill commands. 181² is 32,761, so dividing an area into 181 × 181 squares will work. If you have an even larger volume, 32³ is 32,768.