diff --git a/files.cpp b/files.cpp
index 58e69cd..58a9b37 100644
--- a/files.cpp
+++ b/files.cpp
@@ -39,41 +39,6 @@ void initFileSystem()
     }
 }
 
-/**
-    * Appends text and a new line to a file
-    * @param filename file name, eg: "output.txt"
-    * @param text the string to append to the end of the file
-    */
-//% blockId="files_append_line" block="file %filename|append line %text"
-//% blockExternalInputs=1 weight=90 blockGap=8
-void appendLine(StringData *filename, StringData *text)
-{
-    initFileSystem();
-    ManagedString fn(filename);
-    ManagedString t(text);
-    MicroBitFile f(fn);
-    f.append(t);
-    f.append("\r\n");
-    f.close();
-}
-
-/**
-    * Appends text to a file
-    * @param filename file name, eg: "output.txt"
-    * @param text the string to append to the end of the file
-    */
-//% blockId="fs_append_string" block="file %filename|append string %text"
-//% blockExternalInputs=1 weight=86 blockGap=8
-void appendString(StringData *filename, StringData *text)
-{
-    initFileSystem();
-    ManagedString fn(filename);
-    ManagedString t(text);
-    MicroBitFile f(fn);
-    f.append(t);
-    f.close();
-}
-
 /**
 * Reads the content of the file to send it to serial
 * @param filename file name, eg: "output.txt"
@@ -223,16 +188,35 @@ Buffer fsReadBuffer(int fd, int length) {
         return mkBuffer(NULL, 0);
 
     initFileSystem();
-    Buffer buf = mkBuffer(NULL, length);
-
+    // compute position, length
+    int pos = MicroBitFileSystem::defaultFileSystem->seek(fd, 0, FileSystemSeekFlags::Current);
+    int end = MicroBitFileSystem::defaultFileSystem->seek(fd, 0, FileSystemSeekFlags::End);
+    MicroBitFileSystem::defaultFileSystem->seek(fd, pos, FileSystemSeekFlags::Set);
+    // cap length
+    length = min(length, end - pos);
+    auto buf = mkBuffer(NULL, length);
     int ret = MicroBitFileSystem::defaultFileSystem->read(fd, PXT_BUFFER_DATA(buf), buf->length);
-
     if (ret < 0) return mkBuffer(NULL, 0);
-    else if (ret != length) {
-        auto sbuf = mkBuffer(PXT_BUFFER_DATA(buf), ret);
-        decrRC(buf);
-        return sbuf;
-    }
+    else return buf;
+}
+
+/**
+*/
+//% weight=0 advanced=true
+String fsReadString(int fd, int length) {
+    if (fd < 0 || length < 0) 
+        return mkString(NULL, 0);
+
+    initFileSystem();    
+    // compute position, length
+    int pos = MicroBitFileSystem::defaultFileSystem->seek(fd, 0, FileSystemSeekFlags::Current);
+    int end = MicroBitFileSystem::defaultFileSystem->seek(fd, 0, FileSystemSeekFlags::End);
+    MicroBitFileSystem::defaultFileSystem->seek(fd, pos, FileSystemSeekFlags::Set);
+    // cap length
+    length = min(length, end - pos);
+    auto buf = mkString(NULL, length);
+    int ret = MicroBitFileSystem::defaultFileSystem->read(fd, (uint8_t*)buf->data, buf->length);
+    if (ret < 0) return mkString(NULL, 0);
     else return buf;
 }
 
diff --git a/files.ts b/files.ts
index a4082ee..5d20f5e 100644
--- a/files.ts
+++ b/files.ts
@@ -3,6 +3,38 @@
 */
 //% weight=5 color=#002050 icon="\uf0a0"
 namespace files {
+    export let NEW_LINE = "\r\n";
+    export let TAB = "\t";
+
+    /**
+     * Appends text and a new line to a file
+     * @param filename file name, eg: "output.txt"
+     * @param text the string to append to the end of the file
+     */
+    //% blockId="files_append_line" block="file %filename|append line %text"
+    //% blockExternalInputs=1 weight=90 blockGap=8
+    export function appendLine(filename: string, text: string): void {
+        const file = open(filename);
+        file.seek(0, FileSystemSeekFlags.End);
+        file.writeString(text);
+        file.writeString(NEW_LINE);
+        file.close();
+    }
+
+    /**
+     * Appends text to a file
+     * @param filename file name, eg: "output.txt"
+     * @param text the string to append to the end of the file
+     */
+    //% blockId="fs_append_string" block="file %filename|append string %text"
+    //% blockExternalInputs=1 weight=86 blockGap=8
+    export function appendString(filename: string, text: string): void {
+        const file = open(filename);
+        file.seek(0, FileSystemSeekFlags.End);
+        file.writeString(text);
+        file.close();
+    }
+
     /**
     * Appends a number to a file
     * @param filename file name, eg: "output.txt"
@@ -11,7 +43,24 @@ namespace files {
     //% blockId="fs_append_number" block="file %filename|append number %value"
     //% blockExternalInputs=1 weight=85
     export function appendNumber(filename: string, value: number) {
-        files.appendString(filename, value.toString());
+        const file = open(filename);
+        file.seek(0, FileSystemSeekFlags.End);
+        file.writeString(value.toString());
+        file.close();
+    }
+
+    /**
+     * Appends a buffer to the end of the file
+     * @param filename 
+     * @param buffer 
+     */
+    //% blockId="fs_append_buffer" block="file %filename|append buffer $buffer"
+    //% weight=84
+    export function appendBuffer(filename: string, buffer: Buffer) {
+        const file = open(filename);
+        file.seek(0, FileSystemSeekFlags.End);
+        file.writeBuffer(buffer);
+        file.close();
     }
 
     /**
@@ -110,7 +159,7 @@ namespace files {
          */
         //% blockGap=8
         //% blockId=fs_file_position block="%this|position" advanced=true
-        public position(): number {
+        public get position(): number {
             return files.fsSeek(this.fd, 0, FileSystemSeekFlags.Current);
         }
 
@@ -120,10 +169,22 @@ namespace files {
          */
         //% blockGap=8 advanced=true
         //% blockId=fs_file_set_position block="%this|set position %position"
-        public setPosition(position: number): void {
+        public set position(position: number) {
             files.fsSeek(this.fd, position, FileSystemSeekFlags.Set);
         }
 
+        /**
+         * Returns the file length in bytes
+         */
+        //% blockGap=8 advanced=true
+        //% blockId=fs_file_length block="%this|length"
+        public get length(): number {
+            files.fsSeek(this.fd, 0, FileSystemSeekFlags.End);
+            const l = files.fsSeek(this.fd, 0, FileSystemSeekFlags.Current);
+            files.fsSeek(this.fd, 0, FileSystemSeekFlags.Set);
+            return l;
+       }
+
         /**
          * Write a string to the file.
          */
@@ -144,14 +205,34 @@ namespace files {
 
         /**
          * Reads the file at the current position and fills a buffer
-         * @param length maximum number of bytes to read, eg: 64
+         * @param length maximum number of bytes to read, if negative reads the entire file eg: 64
          */
         //% blockGap=8
-        //% blockId=fs_file_read_buffer block="%this|read buffer (bytes) %length" advanced=true
+        //% blockId=fs_file_read_buffer block="%this|read buffer $length (bytes)" advanced=true
         public readBuffer(length: number): Buffer {
+            const p = this.position;
+            const l = this.length;
+            if (length < 0)
+                length = l;
+            length = Math.min(length, l - p);
             return files.fsReadBuffer(this.fd, length);
         }
 
+        /**
+         * Reads the file at the current position and a string.
+         * @param length maximum number of bytes to read, if negative reads the entire file eg: 64
+         */
+        //% blockGap=8
+        //% blockId=fs_file_read_string block="%this|read string $length (chars)" advanced=true
+        public readString(length: number): String {
+            const p = this.position;
+            const l = this.length;
+            if (length < 0)
+                length = l;
+            length = Math.min(length, l - p);
+            return files.fsReadString(this.fd, length);
+        }
+
         /**
          * Reads the next character in the file at the current position
          */
@@ -160,5 +241,41 @@ namespace files {
         public read(): number {
             return files.fsRead(this.fd);
         }
+
+        /**
+         * Reads the next line in the file at the current position
+         */
+        //% blockGap=8
+        //% blockId=fs_file_read_line block="%this|read line" advanced=true
+        public readLine(): string {
+            const nl = NEW_LINE;
+            const length = this.length;
+            const start = this.position;
+            // scan until new line or eol
+            let end = start;
+            while (end < length) {
+                let c = this.read();
+                if (c == 13 /* \r */ && this.position < length) {
+                    // try scanning for next character
+                    c = this.read();
+                }
+                if (c == 10 /* \n */) {
+                    // found a new line
+                    break;
+                }
+                // update end position
+                end = this.position;
+            }
+
+            // end of file shortcut
+            if (start == end) return "";
+
+            // remember current position
+            const pos = this.position;
+            this.position = start; // reset current cursor
+            const line = fsReadString(this.fd, end - start); // read line
+            this.position = pos; // skip new line
+            return line;
+        }
     }
 }
diff --git a/shims.d.ts b/shims.d.ts
index 42110dd..325fdc6 100644
--- a/shims.d.ts
+++ b/shims.d.ts
@@ -7,24 +7,6 @@
     //% weight=5 color=#002050 icon="\uf0a0"
 declare namespace files {
 
-    /**
-     * Appends text and a new line to a file
-     * @param filename file name, eg: "output.txt"
-     * @param text the string to append to the end of the file
-     */
-    //% blockId="files_append_line" block="file %filename|append line %text"
-    //% blockExternalInputs=1 weight=90 blockGap=8 shim=files::appendLine
-    function appendLine(filename: string, text: string): void;
-
-    /**
-     * Appends text to a file
-     * @param filename file name, eg: "output.txt"
-     * @param text the string to append to the end of the file
-     */
-    //% blockId="fs_append_string" block="file %filename|append string %text"
-    //% blockExternalInputs=1 weight=86 blockGap=8 shim=files::appendString
-    function appendString(filename: string, text: string): void;
-
     /**
      * Reads the content of the file to send it to serial
      * @param filename file name, eg: "output.txt"
@@ -104,6 +86,11 @@ declare namespace files {
     //% weight=0 advanced=true shim=files::fsReadBuffer
     function fsReadBuffer(fd: int32, length: int32): Buffer;
 
+    /**
+     */
+    //% weight=0 advanced=true shim=files::fsReadString
+    function fsReadString(fd: int32, length: int32): string;
+
     /**
      *
      */
diff --git a/tests.ts b/tests.ts
index 823f8da..e4afb29 100644
--- a/tests.ts
+++ b/tests.ts
@@ -1,66 +1,86 @@
 let fi = 0;
-let file = "";
-input.onButtonPressed(Button.B, () => {
-    file = "data" + (fi++) + ".csv";
-    serial.writeLine(file);
-    files.remove(file)
-    files.readToSerial(file);
+{   // settings
+    console.log("settings");
+    fi++;
+    let test = Math.randomRange(0, 1000);
+    files.settingsSaveNumber("test", test);
+    serial.writeValue("test", test);
+    let serTest = files.settingsReadNumber("test");
+    serial.writeValue("serTest", serTest);
+    control.assert(test == serTest);
+}
+
+{   // readline
+    console.log("append")
+    const fn = "test" + (fi++) + ".txt";
+    let expected = "";
+    const r = Math.random().toString();
+    const n = 3;
+    serial.writeValue("expected lines", n);
+    for (let i = 0; i < n; ++i) {
+        files.appendLine(fn, r);
+        expected += r + files.NEW_LINE;
+    }
+
+    { // readString
+        let actual = files.open(fn).readString(-1);
+        serial.writeLine("readstring: " + actual);
+        control.assert(expected == actual);
+    }
+
+    { // readline
+        let actual = "";
+        let line = "";
+        const f = files.open(fn);
+        let i = 0;
+        do {
+            line = f.readLine();
+            actual += line + files.NEW_LINE;
+            i++;
+        } while (line.length)
+        serial.writeValue("actual lines", i);
+        control.assert(n == i);
+        serial.writeLine("readline: " + actual);
+        control.assert(expected == actual);
+    }
+}
+
+{   // file append line
+    console.log("file")
+    const fn = "test" + (fi++) + ".txt";
+    let f = files.open(fn);
+    const expected = "writeString\r\n";
+    f.writeString(expected);
+    f.seek(0, FileSystemSeekFlags.End);
+    f.flush();
+    f.close();
+    let actual = files.open(fn).readString(-1);
+    control.assert(expected == actual);
+}
+
+{   // stress
+    console.log("stress")
+    const fn = "test" + (fi++) + ".txt";
+    serial.writeLine(fn);
+    files.remove(fn)
+    files.readToSerial(fn);
     serial.writeLine("");
     basic.showString("o")
+    const buf = control.createBuffer(4);
+    buf.setNumber(NumberFormat.UInt32LE, 0, ~0);
     for (let i = 0; i < 200; ++i) {
         let t = input.runningTime();
         let ay = input.acceleration(Dimension.Y);
-        files.appendNumber(file, i);
-        files.appendString(file, " ");
-        files.appendNumber(file, i * i);
-        files.appendLine(file, "");
+        files.appendNumber(fn, i);
+        files.appendString(fn, " ");
+        files.appendNumber(fn, i * i);
+        files.appendLine(fn, "");
+        files.appendBuffer(fn, buf);
+        files.appendLine(fn, "");
         serial.writeLine(".")
         basic.pause(10)
     }
     serial.writeLine("");
-    files.readToSerial(file);
+    files.readToSerial(fn);
     basic.showString(":)")
-})
-let test = Math.randomRange(0, 1000);
-files.settingsSaveNumber("test", test);
-serial.writeValue("test", test);
-let serTest = files.settingsReadNumber("test");
-serial.writeValue("serTest", serTest);
-control.assert(test == serTest);
-
-let f = files.open("output.txt");
-f.writeString("writeString\r\n");
-f.seek(0, FileSystemSeekFlags.End);
-f.flush();
-f.close();
-
-input.onButtonPressed(Button.A, () => {
-    files.appendLine(
-        "output.txt",
-        "hello"
-    )
-})
-input.onButtonPressed(Button.B, () => {
-    basic.showString("H")
-    files.readToSerial("output.txt")
-    serial.writeString("Hi")
-})
-
-const fn = "out2.txt";
-input.onButtonPressed(Button.A, () => {
-    basic.showString("o")
-    files.appendLine(fn, "hello");
-    serial.writeString("[")
-    files.readToSerial(fn)
-})
-const fo = "output.txt";
-input.onButtonPressed(Button.A, () => {
-    files.appendLine(fo, "hello")
-    serial.writeString("W")
-    basic.showString("W")
-})
-input.onButtonPressed(Button.B, () => {
-    files.readToSerial(fo)
-    serial.writeString("Hi")
-    basic.showString("H")
-})
+}
diff --git a/tsconfig.json b/tsconfig.json
index 1ba59f2..a2079ff 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -4,5 +4,6 @@
         "noImplicitAny": true,
         "outDir": "built",
         "rootDir": "."
-    }
+    },
+    "exclude": ["pxt_modules/**/*test.ts"]
 }