core-bundle/src/Resources/contao/library/Contao/File.php
protected function fputs($varData, $strMode)
	{
		if (!\is_resource($this->resFile))
		{
			$this->strTmp = 'system/tmp/' . md5(uniqid(mt_rand(), true));

			// Copy the contents of the original file to append data
			if (strncmp($strMode, 'a', 1) === 0 && file_exists($this->strRootDir . '/' . $this->strFile))
			{
				$this->Files->copy($this->strFile, $this->strTmp);
			}

			// Open the temporary file
			if (!$this->resFile = $this->Files->fopen($this->strTmp, $strMode))
			{
				return false;
			}
		}

		fwrite($this->resFile, $varData);

		return true;
	}
protected function fputs($varData, $strMode)
	{
		if (!\is_resource($this->resFile))
		{
			$this->strTmp = 'system/tmp/' . md5(uniqid(mt_rand(), true));

			// Copy the contents of the original file to append data
			if (strncmp($strMode, 'a', 1) === 0 && file_exists($this->strRootDir . '/' . $this->strFile))
			{
				$this->Files->copy($this->strFile, $this->strTmp);
			}

			// Open the temporary file
			if (!$this->resFile = $this->Files->fopen($this->strTmp, $strMode))
			{
				return false;
			}
		}

		fwrite($this->resFile, $varData);

		return true;
	}
Write data to a file

@param mixed  $varData The data to be written
@param string $strMode The operation mode

@return boolean True if the operation was successful