I said, added a command!

src/main/java/io/github/thebusybiscuit/slimefun4/core/commands/subcommands/BackpackCommand.java

@@ -1,4 +1,76 @@
 package io.github.thebusybiscuit.slimefun4.core.commands.subcommands;
 
-public class BackpackCommand {
+import io.github.thebusybiscuit.slimefun4.api.player.PlayerBackpack;
+import io.github.thebusybiscuit.slimefun4.api.player.PlayerProfile;
+import io.github.thebusybiscuit.slimefun4.core.commands.SlimefunCommand;
+import io.github.thebusybiscuit.slimefun4.core.commands.SubCommand;
+import me.mrCookieSlime.Slimefun.Lists.SlimefunItems;
+import me.mrCookieSlime.Slimefun.SlimefunPlugin;
+import me.mrCookieSlime.Slimefun.api.Slimefun;
+import org.bukkit.Bukkit;
+import org.bukkit.ChatColor;
+import org.bukkit.OfflinePlayer;
+import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.meta.ItemMeta;
+
+import java.util.List;
+
+class BackpackCommand extends SubCommand {
+
+    BackpackCommand(SlimefunPlugin plugin, SlimefunCommand cmd) {
+        super(plugin, cmd);
+    }
+
+    @Override
+    public String getName() {
+        return "backpack";
+    }
+
+    @Override
+    public boolean isHidden() {
+        return false;
+    }
+
+    @Override
+    public void onExecute(CommandSender sender, String[] args) {
+        if (!(sender instanceof Player) || !(sender.hasPermission("slimefun.command.backpack"))) {
+            SlimefunPlugin.getLocal().sendMessage(sender, "messages.no-permission", true);
+            return;
+        }
+        if (args.length != 3) {
+            SlimefunPlugin.getLocal().sendMessage(sender, "messages.usage", true, msg -> msg.replace("%usage%", "/sf backpack <Player> <Number>"));
+            return;
+        }
+
+        Player p = (Player) sender;
+        String ownerName = args[1];
+        int id = Integer.parseInt(args[2]);
+        OfflinePlayer owner = Bukkit.getPlayer(ownerName);
+
+        if (owner == null) {
+            owner = Bukkit.getOfflinePlayer(ownerName);
+            if (!owner.hasPlayedBefore()) {
+                SlimefunPlugin.getLocal().sendMessage(sender, "guide.backpack.player-never-joined");
+                return;
+            }
+        }
+
+        PlayerProfile.get(owner, profile -> {
+            if (!profile.getBackpack(id).isPresent()) {
+                SlimefunPlugin.getLocal().sendMessage(sender, "guide.backpack.backpack-does-not-exist");
+                return;
+            }
+            PlayerBackpack bp = profile.getBackpack(id).get();
+            //No point switching for size, would still miss soulbound
+            ItemStack item = SlimefunItems.BACKPACK_MEDIUM;
+            ItemMeta meta = item.getItemMeta();
+            List lore = meta.getLore();
+            lore.set(2, ChatColor.GRAY + "ID: " + profile.getUUID().toString() + "#" + id);
+            meta.setLore(lore);
+            item.setItemMeta(meta);
+            Slimefun.runSync(() -> p.getInventory().addItem(item));
+        });
+    }
 }

src/main/java/io/github/thebusybiscuit/slimefun4/core/commands/subcommands/Commands.java

@@ -25,5 +25,6 @@ public final class Commands {
         commands.add(new OpenGuideCommand(plugin, cmd));
         commands.add(new SearchCommand(plugin, cmd));
         commands.add(new DebugFishCommand(plugin, cmd));
+        commands.add(new BackpackCommand(plugin,cmd));
     }
 }

src/main/resources/languages/messages_en.yml

@@ -2,6 +2,7 @@ commands:
   help: Displays this help screen
   cheat: Allows you to cheat Items
   give: Give somebody some Slimefun Items
+  backpack: Retrieve an existing backpack
   guide: Gives yourself a Slimefun Guide
   timings: Lag-Info about your Server
   teleporter: See other Player's Waypoints
@@ -43,6 +44,10 @@ guide:
   cheat:
     no-multiblocks: '&4You cannot cheat in Multiblocks, you have to build them!'
 
+  backpack:
+    player-never-joined: '&4No player with that name has ever joined the server!'
+    backpack-does-not-exist: '&4That backpack does not exist!'
+  
   pages:
     previous: 'Previous page'
     next: 'Next page'

src/main/resources/plugin.yml

@@ -37,6 +37,9 @@ permissions:
   slimefun.command.versions:
     description: Allows you to do /sf versions
     default: op
+  slimefun.command.backpack:
+    description: Allows you to do /sf backpack
+    default: op
   slimefun.command.guide:
     description: Allows you to obtain the Slimefun guide book
     default: true