diff --git a/bin/generate-document b/bin/generate-document
index a68a1361..10ac8118 100755
--- a/bin/generate-document
+++ b/bin/generate-document
@@ -1,13 +1,23 @@
 #!/usr/bin/env php
 <?php
 
+use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
 use PhpOffice\PhpSpreadsheet\DocumentGenerator;
 
 require_once __DIR__ . '/../src/Bootstrap.php';
 
 try {
-    DocumentGenerator::generateFunctionListByCategory();
-    DocumentGenerator::generateFunctionListByName();
+    $phpSpreadsheetFunctionsProperty = (new ReflectionClass(Calculation::class))->getProperty('phpSpreadsheetFunctions');
+    $phpSpreadsheetFunctionsProperty->setAccessible(true);
+    $phpSpreadsheetFunctions = $phpSpreadsheetFunctionsProperty->getValue();
+    ksort($phpSpreadsheetFunctions);
+
+    file_put_contents(__DIR__ . '/../docs/references/function-list-by-category.md',
+        DocumentGenerator::generateFunctionListByCategory($phpSpreadsheetFunctions)
+    );
+    file_put_contents(__DIR__ . '/../docs/references/function-list-by-name.md',
+        DocumentGenerator::generateFunctionListByName($phpSpreadsheetFunctions)
+    );
 } catch (ReflectionException $e) {
     fwrite(STDERR, (string)$e);
     exit(1);
diff --git a/src/PhpSpreadsheet/DocumentGenerator.php b/src/PhpSpreadsheet/DocumentGenerator.php
index 010d1325..de6f313f 100644
--- a/src/PhpSpreadsheet/DocumentGenerator.php
+++ b/src/PhpSpreadsheet/DocumentGenerator.php
@@ -1,64 +1,69 @@
 <?php
 
-
 namespace PhpOffice\PhpSpreadsheet;
 
-
-use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
 use PhpOffice\PhpSpreadsheet\Calculation\Category;
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
 use ReflectionClass;
 use ReflectionException;
 use UnexpectedValueException;
 
-class DocumentGenerator {
+class DocumentGenerator
+{
     /**
+     * @param array[] $phpSpreadsheetFunctions
+     *
      * @throws ReflectionException
+     *
+     * @return string
      */
-    public static function generateFunctionListByCategory(): void {
-        ob_start();
-        try {
-            echo "# Function list by category\n";
-            $phpSpreadsheetFunctions = self::getPhpSpreadsheetFunctions();
-            foreach (self::getCategories() as $categoryConstant => $category) {
-                echo "\n";
-                echo "## {$categoryConstant}\n";
-                echo "\n";
-                echo "Excel Function      | PhpSpreadsheet Function\n";
-                echo "--------------------|-------------------------------------------\n";
-                foreach ($phpSpreadsheetFunctions as $function => $functionInfo) {
-                    if ($category === $functionInfo['category']) {
-                        echo str_pad($function, 20)
-                            . '| ' . self::getPhpSpreadsheetFunctionText($functionInfo['functionCall']) . "\n";
-                    }
+    public static function generateFunctionListByCategory(array $phpSpreadsheetFunctions): string
+    {
+        $result = "# Function list by category\n";
+        foreach (self::getCategories() as $categoryConstant => $category) {
+            $result .= "\n";
+            $result .= "## {$categoryConstant}\n";
+            $result .= "\n";
+            $lengths = [20, 42];
+            $result .= self::tableRow($lengths, ['Excel Function', 'PhpSpreadsheet Function']) . "\n";
+            $result .= self::tableRow($lengths, null) . "\n";
+            foreach ($phpSpreadsheetFunctions as $excelFunction => $functionInfo) {
+                if ($category === $functionInfo['category']) {
+                    $phpFunction = self::getPhpSpreadsheetFunctionText($functionInfo['functionCall']);
+                    $result .= self::tableRow($lengths, [$excelFunction, $phpFunction]) . "\n";
                 }
             }
-        } finally {
-            file_put_contents(__DIR__ . '/../../docs/references/function-list-by-category.md', ob_get_clean());
         }
+
+        return $result;
     }
 
     /**
-     * @return mixed
      * @throws ReflectionException
-     */
-    private static function getPhpSpreadsheetFunctions() {
-        $phpSpreadsheetFunctionsProperty = (new ReflectionClass(Calculation::class))->getProperty('phpSpreadsheetFunctions');
-        $phpSpreadsheetFunctionsProperty->setAccessible(true);
-        $phpSpreadsheetFunctions = $phpSpreadsheetFunctionsProperty->getValue();
-        ksort($phpSpreadsheetFunctions);
-        return $phpSpreadsheetFunctions;
-    }
-
-    /**
+     *
      * @return array
-     * @throws ReflectionException
      */
-    private static function getCategories(): array {
+    private static function getCategories(): array
+    {
         return (new ReflectionClass(Category::class))->getConstants();
     }
 
-    private static function getPhpSpreadsheetFunctionText($functionCall): string {
+    private static function tableRow(array $lengths, array $values = null): string
+    {
+        $result = '';
+        foreach (array_map(null, $lengths, $values ?? []) as $i => [$length, $value]) {
+            $pad = $value === null ? '-' : ' ';
+            if ($i > 0) {
+                $result .= '|' . $pad;
+            }
+            $result .= str_pad($value ?? '', $length, $pad);
+        }
+
+        return rtrim($result, ' ');
+    }
+
+    private static function getPhpSpreadsheetFunctionText($functionCall): string
+    {
         if (is_string($functionCall)) {
             return $functionCall;
         }
@@ -68,35 +73,39 @@ class DocumentGenerator {
         if (is_array($functionCall)) {
             return "\\{$functionCall[0]}::{$functionCall[1]}";
         }
-        throw new UnexpectedValueException('$functionCall is of type ' . gettype($functionCall) . '. string or array expected');
+
+        throw new UnexpectedValueException(
+            '$functionCall is of type ' . gettype($functionCall) . '. string or array expected'
+        );
     }
 
     /**
+     * @param array[] $phpSpreadsheetFunctions
+     *
      * @throws ReflectionException
+     *
+     * @return string
      */
-    public static function generateFunctionListByName(): void {
+    public static function generateFunctionListByName(array $phpSpreadsheetFunctions): string
+    {
         $categoryConstants = array_flip(self::getCategories());
-        ob_start();
-        try {
-            echo "# Function list by name\n";
-            $phpSpreadsheetFunctions = self::getPhpSpreadsheetFunctions();
-            $lastAlphabet = null;
-            foreach ($phpSpreadsheetFunctions as $function => $functionInfo) {
-                if ($lastAlphabet !== $function[0]) {
-                    $lastAlphabet = $function[0];
-                    echo "\n";
-                    echo "## {$lastAlphabet}\n";
-                    echo "\n";
-                    echo "Excel Function      | Category                       | PhpSpreadsheet Function\n";
-                    echo "--------------------|--------------------------------|-------------------------------------------\n";
-                }
-                echo str_pad($function, 20)
-                    . '| ' . str_pad($categoryConstants[$functionInfo['category']], 31)
-                    . '| ' . self::getPhpSpreadsheetFunctionText($functionInfo['functionCall'])
-                    . "\n";
+        $result = "# Function list by name\n";
+        $lastAlphabet = null;
+        foreach ($phpSpreadsheetFunctions as $excelFunction => $functionInfo) {
+            $lengths = [20, 31, 42];
+            if ($lastAlphabet !== $excelFunction[0]) {
+                $lastAlphabet = $excelFunction[0];
+                $result .= "\n";
+                $result .= "## {$lastAlphabet}\n";
+                $result .= "\n";
+                $result .= self::tableRow($lengths, ['Excel Function', 'Category', 'PhpSpreadsheet Function']) . "\n";
+                $result .= self::tableRow($lengths, null) . "\n";
             }
-        } finally {
-            file_put_contents(__DIR__ . '/../../docs/references/function-list-by-name.md', ob_get_clean());
+            $category = $categoryConstants[$functionInfo['category']];
+            $phpFunction = self::getPhpSpreadsheetFunctionText($functionInfo['functionCall']);
+            $result .= self::tableRow($lengths, [$excelFunction, $category, $phpFunction]) . "\n";
         }
+
+        return $result;
     }
-}
\ No newline at end of file
+}