minecraft-assets/data/minecraft/recipes/rail.json

{
  "type": "minecraft:crafting_shaped",
  "category": "misc",
  "key": {
    "#": {
      "item": "minecraft:stick"
    },
    "X": {
      "item": "minecraft:iron_ingot"
    }
  },
  "pattern": [
    "X X",
    "X#X",
    "X X"
  ],
  "result": {
    "count": 16,
    "item": "minecraft:rail"
  }
}