First init.

libraries/SD/examples/listfiles/listfiles.ino

@@ -0,0 +1,86 @@
+/*
+  Listfiles
+
+  This example shows how to print out the files in a
+  directory on a SD card. Pin numbers reflect the default
+  SPI pins for Uno and Nano models
+
+  The circuit:
+   SD card attached to SPI bus as follows:
+ ** SDO - pin 11
+ ** SDI - pin 12
+ ** CLK - pin 13
+ ** CS - depends on your SD card shield or module.
+ 		Pin 10 used here for consistency with other Arduino examples
+    (for MKR Zero SD: SDCARD_SS_PIN)
+
+  created   Nov 2010
+  by David A. Mellis
+  modified 9 Apr 2012
+  by Tom Igoe
+  modified 2 Feb 2014
+  by Scott Fitzgerald
+  modified 24 July 2020
+  by Tom Igoe
+  
+  This example code is in the public domain.
+
+*/
+#include <SD.h>
+
+const int chipSelect = 10;
+File root;
+
+void setup() {
+ // Open serial communications and wait for port to open:
+  Serial.begin(9600);
+  // wait for Serial Monitor to connect. Needed for native USB port boards only:
+  while (!Serial);
+
+  Serial.print("Initializing SD card...");
+
+  if (!SD.begin(chipSelect)) {
+    Serial.println("initialization failed. Things to check:");
+    Serial.println("1. is a card inserted?");
+    Serial.println("2. is your wiring correct?");
+    Serial.println("3. did you change the chipSelect pin to match your shield or module?");
+    Serial.println("Note: press reset button on the board and reopen this Serial Monitor after fixing your issue!");
+    while (true);
+  }
+
+  Serial.println("initialization done.");
+
+  root = SD.open("/");
+
+  printDirectory(root, 0);
+
+  Serial.println("done!");
+}
+
+void loop() {
+  // nothing happens after setup finishes.
+}
+
+void printDirectory(File dir, int numTabs) {
+  while (true) {
+
+    File entry =  dir.openNextFile();
+    if (! entry) {
+      // no more files
+      break;
+    }
+    for (uint8_t i = 0; i < numTabs; i++) {
+      Serial.print('\t');
+    }
+    Serial.print(entry.name());
+    if (entry.isDirectory()) {
+      Serial.println("/");
+      printDirectory(entry, numTabs + 1);
+    } else {
+      // files have sizes, directories do not
+      Serial.print("\t\t");
+      Serial.println(entry.size(), DEC);
+    }
+    entry.close();
+  }
+}