Recipes

GTCEu has a great recipe structure. Adding and removing is pretty much the same for each machine. Recipes for a machine are stored in a RecipeMap. You can get a recipe map like this:

groovy

def recipeMap = mods.gregtech.recipe_map_name
// this works also:
def recipeMap2 = recipemap('recipe_map_name')

You can find a list of all machines here.
Let's use alloy_smelter as an example here. With the recipe map you can create a recipe builder.

groovy

mods.gregtech.alloy_smelter.recipeBuilder()

You don't know what a builder is? Check this out.

Builder functions

GregTechs recipe builder has tons of helper functions. We'll only focus on the important ones.

Adding inputs

Works for fluid and items

groovy

inputs(IIngredient ingredient)
inputs(IIngredient... ingredients)
inputs(Collection<IIngredient> ingredients)
notConsumable(IIngredient ingredient) // this will not be consumed

Adding outputs

groovy

outputs(ItemStack)
outputs(ItemStack...)
outputs(Collection<ItemStack>)
chancedOutput(ItemStack, int chance, int tierChanceBoost) // this will not be consumed

fluidOutputs(FluidStack)
fluidOutputs(FluidStack...)
fluidOutputs(Collection<FluidStack>)

Other

groovy

duration(int duration) // base recipe duration int ticks (20 ticks = 1 sec)
EUt(int EUt)
hidden() // hides recipe in jei

cleanroom(CleanroomType) // makes the recipe require cleanroom

Register recipe

groovy

buildAndRegister()

Example

groovy

import gregtech.api.metatileentity.multiblock.CleanroomType // needed when you want to use cleanroom

mods.gregtech.alloy_smelter.recipeBuilder()
    .inputs(item('minecraft:dirt'), ore('stone'))
    .outputs(item('minecraft:nether_star') * 2)
    .cleanroom(CleanroomType.CLEANROOM) // CLEANROOM and STERILE_CLEANROOM are valid
    .duration(200) // 10 seconds
    .EUt(512) // HV recipe
    .buildAndRegister()