![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2023\/07\/ESP32-Write-Data-To-a-File-LittleFS.jpg?resize=1200%2C675&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\nWe have a similar tutorial for ESP8266 boards: ESP8266 NodeMCU: Write Data to a File (LittleFS) \u2013 Arduino IDE<\/a>.<\/p>\n\n\n\n Table of Contents<\/strong><\/p>\n\n\n\n Throughout this tutorial, we’ll cover the following topics:<\/p>\n\n\n\n We\u2019ll program the ESP32 board using Arduino IDE. So, make sure you have the ESP32 add-on installed. Follow the next tutorial if you haven’t already:<\/p>\n\n\n\n Additionally, make sure you’re running the latest version of the ESP32 add-on. Go to Tools <\/strong>> Board <\/strong>> Boards Manager,<\/strong> search for ESP32, <\/strong>and check that you’re running the latest version.<\/p>\n\n\n\n LittleFS is a lightweight filesystem created for microcontrollers that lets you access the flash memory like you would do in a standard file system on your computer, but it\u2019s simpler and more limited. You can read, write, close, and delete files and folders. Using a filesystem with the ESP32 boards is especially useful to:<\/p>\n\n\n\n You may also like reading: ESP32: Upload Files to LittleFS using Arduino IDE<\/a>.<\/p>\n\n\n\n Before showing you how to write data to a file on LittleFS with the ESP32, let’s take a look at an example that shows how to do practically any task that you may need when dealing with files and folders.<\/p>\n\n\n\n The following code was adapted from the official example<\/a>.<\/p>\n\n\n View raw code<\/a><\/p>\n\n\n\n This code covers the following:<\/p>\n\n\n\n First, you need to include the following libraries: FS.h<\/span> to handle files, and LittleFS.h<\/span> to create and access the filesystem.<\/p>\n\n\n\n The first time you use LittleFS on the ESP32, you need to format it so that it creates a partition dedicated to that filesystem. To do that, we have the following boolean variable to control whether we want to format the filesystem or not.<\/p>\n\n\n\n The example provides several functions to handle files on the LittleFS filesystem. Let’s take a look at them.<\/p>\n\n\n\n The listDir()<\/span> function lists the directories on the filesystem. This function accepts as arguments the filesystem (LittleFs<\/span>), the main directory’s name, and the levels to go into the directory.<\/p>\n\n\n\n Here’s an example of how to call this function. The \/<\/span> corresponds to the root directory. The following command will list all the directories up to one level beginning at the root directory.<\/p>\n\n\n\n The createDir()<\/span> function creates a new directory. Pass as an argument the LittleFS<\/span> filesystem and the directory name path.<\/p>\n\n\n\n For example, the following command creates a new directory (folder) on the root called mydir<\/span>.<\/p>\n\n\n\n To remove a directory from the filesystemca, use the removeDir()<\/span> function and pass as an argument the LittleFS<\/span> filesystem and the directory name path.<\/p>\n\n\n\n Here is an example that deletes the mydir <\/em>folder.<\/p>\n\n\n\n The readFile()<\/span> function reads the content of a file and prints the content in the Serial Monitor. As with previous functions, pass as an argument the LittleFs<\/span> filesystem and the file path.<\/p>\n\n\n\n For example, the following line reads the content of the hello.txt<\/span> file.<\/p>\n\n\n\n To write content to a file, you can use the writeFile()<\/span> function. Pass as an argument, the LittleFS<\/span> filesystem, the file path, and the message (as a const char variable). <\/p>\n\n\n\n The following line writes Hello <\/span> in the hello.txt<\/span> file.<\/p>\n\n\n\n Similarly, you can append content to a file (without overwriting previous content) using the appendFile()<\/span> function.<\/p>\n\n\n\n The following line appends the message World!\\r\\n<\/span> in the hello.txt<\/span> file. The \\r\\n<\/span> means that the next time you write something to the file, it will be written in a new line.<\/p>\n\n\n\n You can rename a file using the renameFile()<\/span> function. Pass as arguments the LittleFS<\/span> filesystem, the original filename, and the new filename.<\/p>\n\n\n\n The following line renames the hello.txt<\/span> file to foo.txt<\/span>.<\/p>\n\n\n\n Use the deleteFile()<\/span> function to delete a file. Pass as an argument the LittleFS<\/span> filesystem and the file path of the file you want to delete.<\/p>\n\n\n\n The following line deletes the foo.txt<\/span> file from the filesystem.<\/p>\n\n\n\n The testFileIO()<\/span> function shows how long it takes to read the content of a file.<\/p>\n\n\n\n The following function tests the test.txt<\/span> file.<\/p>\n\n\n\n In the setup()<\/span>, the following lines initialize the LittleFS filesystem.<\/p>\n\n\n\n The LittleFS.begin()<\/span> function returns true<\/span> if the filesystem is initialized successfully or false<\/span> if it isn’t. <\/p>\n\n\n\n You can pass true<\/span> or false<\/span> as an argument to the begin()<\/span> method. If you pass true<\/span> it will format the LittleFS filesystem if the initialization fails. Because this is the first test we’re running, we set the FORMAT_LITTLEFS_IF_FAILED<\/span> variable to true<\/span>.<\/p>\n\n\n\n The following lines call all the functions we’ve seen previously.<\/p>\n\n\n\n Upload the previous sketch to your ESP32 board. After that, open the Serial Monitor and press the ESP32 on-board RST button. If the initialization succeeds, you’ll get similar messages on the Serial Monitor.<\/p>\n\n\n The previous example illustrated almost all the operations you might need to do when dealing with files and folders on the filesystem. In this section, we’ll take a look at a more simple and specific example: how to save the content of a variable to the filesystem.<\/p>\n\n\n\n Let’s take a look at the following code.<\/p>\n\n\n\n
Prerequisites<\/h2>\n\n\n\n
\n
Introducing LittleFS<\/h2>\n\n\n\n
\n
ESP32 with LittleFS – Handling Files and Folders<\/h2>\n\n\n\n
\/\/ Adapted from: https:\/\/github.com\/espressif\/arduino-esp32\/blob\/master\/libraries\/LittleFS\/examples\/LITTLEFS_test\/LITTLEFS_test.ino\n\/\/ Project details: https:\/\/RandomNerdTutorials.com\/esp32-write-data-littlefs-arduino\/\n\n#include <Arduino.h>\n#include "FS.h"\n#include <LittleFS.h>\n\n\/\/ You only need to format LittleFS the first time you run a\n\/\/ test or else use the LITTLEFS plugin to create a partition \n\/\/ https:\/\/github.com\/lorol\/arduino-esp32littlefs-plugin\n\n#define FORMAT_LITTLEFS_IF_FAILED true\n\nvoid listDir(fs::FS &fs, const char * dirname, uint8_t levels){\n Serial.printf("Listing directory: %s\\r\\n", dirname);\n\n File root = fs.open(dirname);\n if(!root){\n Serial.println("- failed to open directory");\n return;\n }\n if(!root.isDirectory()){\n Serial.println(" - not a directory");\n return;\n }\n\n File file = root.openNextFile();\n while(file){\n if(file.isDirectory()){\n Serial.print(" DIR : ");\n Serial.println(file.name());\n if(levels){\n listDir(fs, file.path(), levels -1);\n }\n } else {\n Serial.print(" FILE: ");\n Serial.print(file.name());\n Serial.print("\\tSIZE: ");\n Serial.println(file.size());\n }\n file = root.openNextFile();\n }\n}\n\nvoid createDir(fs::FS &fs, const char * path){\n Serial.printf("Creating Dir: %s\\n", path);\n if(fs.mkdir(path)){\n Serial.println("Dir created");\n } else {\n Serial.println("mkdir failed");\n }\n}\n\nvoid removeDir(fs::FS &fs, const char * path){\n Serial.printf("Removing Dir: %s\\n", path);\n if(fs.rmdir(path)){\n Serial.println("Dir removed");\n } else {\n Serial.println("rmdir failed");\n }\n}\n\nvoid readFile(fs::FS &fs, const char * path){\n Serial.printf("Reading file: %s\\r\\n", path);\n\n File file = fs.open(path);\n if(!file || file.isDirectory()){\n Serial.println("- failed to open file for reading");\n return;\n }\n\n Serial.println("- read from file:");\n while(file.available()){\n Serial.write(file.read());\n }\n file.close();\n}\n\nvoid writeFile(fs::FS &fs, const char * path, const char * message){\n Serial.printf("Writing file: %s\\r\\n", path);\n\n File file = fs.open(path, FILE_WRITE);\n if(!file){\n Serial.println("- failed to open file for writing");\n return;\n }\n if(file.print(message)){\n Serial.println("- file written");\n } else {\n Serial.println("- write failed");\n }\n file.close();\n}\n\nvoid appendFile(fs::FS &fs, const char * path, const char * message){\n Serial.printf("Appending to file: %s\\r\\n", path);\n\n File file = fs.open(path, FILE_APPEND);\n if(!file){\n Serial.println("- failed to open file for appending");\n return;\n }\n if(file.print(message)){\n Serial.println("- message appended");\n } else {\n Serial.println("- append failed");\n }\n file.close();\n}\n\nvoid renameFile(fs::FS &fs, const char * path1, const char * path2){\n Serial.printf("Renaming file %s to %s\\r\\n", path1, path2);\n if (fs.rename(path1, path2)) {\n Serial.println("- file renamed");\n } else {\n Serial.println("- rename failed");\n }\n}\n\nvoid deleteFile(fs::FS &fs, const char * path){\n Serial.printf("Deleting file: %s\\r\\n", path);\n if(fs.remove(path)){\n Serial.println("- file deleted");\n } else {\n Serial.println("- delete failed");\n }\n}\n\nvoid testFileIO(fs::FS &fs, const char * path){\n Serial.printf("Testing file I\/O with %s\\r\\n", path);\n\n static uint8_t buf[512];\n size_t len = 0;\n File file = fs.open(path, FILE_WRITE);\n if(!file){\n Serial.println("- failed to open file for writing");\n return;\n }\n\n size_t i;\n Serial.print("- writing" );\n uint32_t start = millis();\n for(i=0; i<2048; i++){\n if ((i & 0x001F) == 0x001F){\n Serial.print(".");\n }\n file.write(buf, 512);\n }\n Serial.println("");\n uint32_t end = millis() - start;\n Serial.printf(" - %u bytes written in %u ms\\r\\n", 2048 * 512, end);\n file.close();\n\n file = fs.open(path);\n start = millis();\n end = start;\n i = 0;\n if(file && !file.isDirectory()){\n len = file.size();\n size_t flen = len;\n start = millis();\n Serial.print("- reading" );\n while(len){\n size_t toRead = len;\n if(toRead > 512){\n toRead = 512;\n }\n file.read(buf, toRead);\n if ((i++ & 0x001F) == 0x001F){\n Serial.print(".");\n }\n len -= toRead;\n }\n Serial.println("");\n end = millis() - start;\n Serial.printf("- %u bytes read in %u ms\\r\\n", flen, end);\n file.close();\n } else {\n Serial.println("- failed to open file for reading");\n }\n}\n\nvoid setup(){\n Serial.begin(115200);\n\n if(!LittleFS.begin(FORMAT_LITTLEFS_IF_FAILED)){\n Serial.println("LittleFS Mount Failed");\n return;\n }\n\n createDir(LittleFS, "\/mydir"); \/\/ Create a mydir folder\n writeFile(LittleFS, "\/mydir\/hello1.txt", "Hello1"); \/\/ Create a hello1.txt file with the content "Hello1"\n listDir(LittleFS, "\/", 1); \/\/ List the directories up to one level beginning at the root directory\n deleteFile(LittleFS, "\/mydir\/hello1.txt"); \/\/delete the previously created file\n removeDir(LittleFS, "\/mydir"); \/\/delete the previously created folder\n listDir(LittleFS, "\/", 1); \/\/ list all directories to make sure they were deleted\n \n writeFile(LittleFS, "\/hello.txt", "Hello "); \/\/Create and write a new file in the root directory\n appendFile(LittleFS, "\/hello.txt", "World!\\r\\n"); \/\/Append some text to the previous file\n readFile(LittleFS, "\/hello.txt"); \/\/ Read the complete file\n renameFile(LittleFS, "\/hello.txt", "\/foo.txt"); \/\/Rename the previous file\n readFile(LittleFS, "\/foo.txt"); \/\/Read the file with the new name\n deleteFile(LittleFS, "\/foo.txt"); \/\/Delete the file\n testFileIO(LittleFS, "\/test.txt"); \/\/Testin\n deleteFile(LittleFS, "\/test.txt"); \/\/Delete the file\n \n Serial.println( "Test complete" ); \n}\n\nvoid loop(){\n\n}\n<\/code><\/pre>\n\t\n
How the Code Works<\/h3>\n\n\n\n
#include \"FS.h\"\n#include <LittleFS.h><\/code><\/pre>\n\n\n\n#define FORMAT_LITTLEFS_IF_FAILED true<\/code><\/pre>\n\n\n\nList a directory<\/h4>\n\n\n\n
void listDir(fs::FS &fs, const char * dirname, uint8_t levels){\n Serial.printf(\"Listing directory: %s\\r\\n\", dirname);\n\n File root = fs.open(dirname);\n if(!root){\n Serial.println(\"- failed to open directory\");\n return;\n }\n if(!root.isDirectory()){\n Serial.println(\" - not a directory\");\n return;\n }\n\n File file = root.openNextFile();\n while(file){\n if(file.isDirectory()){\n Serial.print(\" DIR : \");\n Serial.println(file.name());\n if(levels){\n listDir(fs, file.path(), levels -1);\n }\n } else {\n Serial.print(\" FILE: \");\n Serial.print(file.name());\n Serial.print(\"\\tSIZE: \");\n Serial.println(file.size());\n }\n file = root.openNextFile();\n }\n}<\/code><\/pre>\n\n\n\nlistDir(LittleFS, \"\/\", 1); \/\/ List the directories up to one level beginning at the root directory<\/code><\/pre>\n\n\n\nCreate a Directory<\/h4>\n\n\n\n
void createDir(fs::FS &fs, const char * path){\n Serial.printf(\"Creating Dir: %s\\n\", path);\n if(fs.mkdir(path)){\n Serial.println(\"Dir created\");\n } else {\n Serial.println(\"mkdir failed\");\n }\n}<\/code><\/pre>\n\n\n\ncreateDir(LittleFS, \"\/mydir\"); \/\/ Create a mydir folder<\/code><\/pre>\n\n\n\nRemove a Directory<\/h4>\n\n\n\n
void removeDir(fs::FS &fs, const char * path){\n Serial.printf(\"Removing Dir: %s\\n\", path);\n if(fs.rmdir(path)){\n Serial.println(\"Dir removed\");\n } else {\n Serial.println(\"rmdir failed\");\n }\n}<\/code><\/pre>\n\n\n\nremoveDir(LittleFS, \"\/mydir\");<\/code><\/pre>\n\n\n\nRead File Content<\/h4>\n\n\n\n
void readFile(fs::FS &fs, const char * path){\n Serial.printf(\"Reading file: %s\\r\\n\", path);\n\n File file = fs.open(path);\n if(!file || file.isDirectory()){\n Serial.println(\"- failed to open file for reading\");\n return;\n }\n\n Serial.println(\"- read from file:\");\n while(file.available()){\n Serial.write(file.read());\n }\n file.close();\n}<\/code><\/pre>\n\n\n\nreadFile(LittleFS, \"\/hello.txt\"); \/\/ Read the complete file<\/code><\/pre>\n\n\n\nWrite Content to a File<\/h4>\n\n\n\n
void writeFile(fs::FS &fs, const char * path, const char * message){\n Serial.printf(\"Writing file: %s\\r\\n\", path);\n\n File file = fs.open(path, FILE_WRITE);\n if(!file){\n Serial.println(\"- failed to open file for writing\");\n return;\n }\n if(file.print(message)){\n Serial.println(\"- file written\");\n } else {\n Serial.println(\"- write failed\");\n }\n file.close();\n}<\/code><\/pre>\n\n\n\nwriteFile(LittleFS, \"\/hello.txt\", \"Hello \");<\/code><\/pre>\n\n\n\nAppend Content to a File<\/h4>\n\n\n\n
void appendFile(fs::FS &fs, const char * path, const char * message){\n Serial.printf(\"Appending to file: %s\\r\\n\", path);\n\n File file = fs.open(path, FILE_APPEND);\n if(!file){\n Serial.println(\"- failed to open file for appending\");\n return;\n }\n if(file.print(message)){\n Serial.println(\"- message appended\");\n } else {\n Serial.println(\"- append failed\");\n }\n file.close();\n}<\/code><\/pre>\n\n\n\nappendFile(LittleFS, \"\/hello.txt\", \"World!\\r\\n\");<\/code><\/pre>\n\n\n\nRename a File<\/h4>\n\n\n\n
void renameFile(fs::FS &fs, const char * path1, const char * path2){\n Serial.printf(\"Renaming file %s to %s\\r\\n\", path1, path2);\n if (fs.rename(path1, path2)) {\n Serial.println(\"- file renamed\");\n } else {\n Serial.println(\"- rename failed\");\n }\n}<\/code><\/pre>\n\n\n\nrenameFile(LittleFS, \"\/hello.txt\", \"\/foo.txt\");<\/code><\/pre>\n\n\n\nDelete a File<\/h4>\n\n\n\n
void deleteFile(fs::FS &fs, const char * path){\n Serial.printf(\"Deleting file: %s\\r\\n\", path);\n if(fs.remove(path)){\n Serial.println(\"- file deleted\");\n } else {\n Serial.println(\"- delete failed\");\n }\n}<\/code><\/pre>\n\n\n\ndeleteFile(LittleFS, \"\/foo.txt\");<\/code><\/pre>\n\n\n\nTest a File<\/h4>\n\n\n\n
void testFileIO(fs::FS &fs, const char * path){\n Serial.printf(\"Testing file I\/O with %s\\r\\n\", path);\n\n static uint8_t buf[512];\n size_t len = 0;\n File file = fs.open(path, FILE_WRITE);\n if(!file){\n Serial.println(\"- failed to open file for writing\");\n return;\n }\n\n size_t i;\n Serial.print(\"- writing\" );\n uint32_t start = millis();\n for(i=0; i<2048; i++){\n if ((i & 0x001F) == 0x001F){\n Serial.print(\".\");\n }\n file.write(buf, 512);\n }\n Serial.println(\"\");\n uint32_t end = millis() - start;\n Serial.printf(\" - %u bytes written in %u ms\\r\\n\", 2048 * 512, end);\n file.close();\n\n file = fs.open(path);\n start = millis();\n end = start;\n i = 0;\n if(file && !file.isDirectory()){\n len = file.size();\n size_t flen = len;\n start = millis();\n Serial.print(\"- reading\" );\n while(len){\n size_t toRead = len;\n if(toRead > 512){\n toRead = 512;\n }\n file.read(buf, toRead);\n if ((i++ & 0x001F) == 0x001F){\n Serial.print(\".\");\n }\n len -= toRead;\n }\n Serial.println(\"\");\n end = millis() - start;\n Serial.printf(\"- %u bytes read in %u ms\\r\\n\", flen, end);\n file.close();\n } else {\n Serial.println(\"- failed to open file for reading\");\n }\n}<\/code><\/pre>\n\n\n\ntestFileIO(LittleFS, \"\/test.txt\"); <\/code><\/pre>\n\n\n\nInitialize the Filesystem<\/h4>\n\n\n\n
if(!LittleFS.begin(FORMAT_LITTLEFS_IF_FAILED)){\n Serial.println(\"LittleFS Mount Failed\");\n return;\n}<\/code><\/pre>\n\n\n\nTesting the Filesystem<\/h4>\n\n\n\n
createDir(LittleFS, \"\/mydir\"); \/\/ Create a mydir folder\nwriteFile(LittleFS, \"\/mydir\/hello1.txt\", \"Hello1\"); \/\/ Create a hello1.txt file with the content \"Hello1\"\nlistDir(LittleFS, \"\/\", 1); \/\/ List the directories up to one level beginning at the root directory\ndeleteFile(LittleFS, \"\/mydir\/hello1.txt\"); \/\/delete the previously created file\nremoveDir(LittleFS, \"\/mydir\"); \/\/delete the previously created folder\nlistDir(LittleFS, \"\/\", 1); \/\/ list all directories to make sure they were deleted\n \nwriteFile(LittleFS, \"\/hello.txt\", \"Hello \"); \/\/Create and write a new file in the root directory\nappendFile(LittleFS, \"\/hello.txt\", \"World!\\r\\n\"); \/\/Append some text to the previous file\nreadFile(LittleFS, \"\/hello.txt\"); \/\/ Read the complete file\nrenameFile(LittleFS, \"\/hello.txt\", \"\/foo.txt\"); \/\/Rename the previous file\nreadFile(LittleFS, \"\/foo.txt\"); \/\/Read the file with the new name\ndeleteFile(LittleFS, \"\/foo.txt\"); \/\/Delete the file\ntestFileIO(LittleFS, \"\/test.txt\"); \/\/Testin\ndeleteFile(LittleFS, \"\/test.txt\"); \/\/Delete the file<\/code><\/pre>\n\n\n\nDemonstration<\/h3>\n\n\n\n
![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2023\/07\/testing-Little-FS-Serial-Monitor.png?resize=601%2C791&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n
\n\n\n\nESP32 with LittleFS – How to Save Variables’ Values to a File<\/h2>\n\n\n\n
\/\/ Project details: https:\/\/RandomNerdTutorials.com\/esp32-write-data-littlefs-arduino\/\n\n#include <Arduino.h>\n#include "FS.h"\n#include <LittleFS.h>\n\n#define FORMAT_LITTLEFS_IF_FAILED true\n\nint mydata;\n\nvoid writeFile(fs::FS &fs, const char * path, const char * message){\n Serial.printf("Writing file: %s\\r\\n", path);\n\n File file = fs.open(path, FILE_WRITE);\n if(!file){\n Serial.println("- failed to open file for writing");\n return;\n }\n if(file.print(message)){\n Serial.println("- file written");\n } else {\n Serial.println("- write failed");\n }\n file.close();\n}\n\nvoid appendFile(fs::FS &fs, const char * path, const char * message){\n Serial.printf("Appending to file: %s\\r\\n", path);\n\n File file = fs.open(path, FILE_APPEND);\n if(!file){\n Serial.println("- failed to open file for appending");\n return;\n }\n if(file.print(message)){\n Serial.println("- message appended");\n } else {\n Serial.println("- append failed");\n }\n file.close();\n}\n\nvoid readFile(fs::FS &fs, const char * path){\n Serial.printf("Reading file: %s\\r\\n", path);\n\n File file = fs.open(path);\n if(!file || file.isDirectory()){\n Serial.println("- failed to open file for reading");\n return;\n }\n\n Serial.println("- read from file:");\n while(file.available()){\n Serial.write(file.read());\n }\n file.close();\n}\n\n\nvoid setup() {\n Serial.begin(115200);\n if(!LittleFS.begin(FORMAT_LITTLEFS_IF_FAILED)){\n Serial.println("LittleFS Mount Failed");\n return;\n }\n else{\n Serial.println("Little FS Mounted Successfully");\n }\n writeFile(LittleFS, "\/data.txt", "MY ESP32 DATA \\r\\n");\n}\n\nvoid loop() {\n mydata = random (0, 1000);\n appendFile(LittleFS, "\/data.txt", (String(mydata)+ "\\r\\n").c_str()); \/\/Append data to the file\n readFile(LittleFS, "\/data.txt"); \/\/ Read the contents of the file\n delay(30000);\n}\n<\/code><\/pre>\n\t
![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2023\/07\/ESP32-LittleFS-Append-Data.png?resize=601%2C732&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n![\"ESP32](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2023\/07\/ESP32-LittleFS-Append-Data-restart.png?resize=601%2C732&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n