system/Log/Logger.php
protected function interpolate($message, array $context = [])
	{
		if (! is_string($message))
		{
			return $message;
		}

		// build a replacement array with braces around the context keys
		$replace = [];

		foreach ($context as $key => $val)
		{
			// Verify that the 'exception' key is actually an exception
			// or error, both of which implement the 'Throwable' interface.
			if ($key === 'exception' && $val instanceof \Throwable)
			{
				$val = $val->getMessage() . ' ' . $this->cleanFileNames($val->getFile()) . ':' . $val->getLine();
			}

			// todo - sanitize input before writing to file?
			$replace['{' . $key . '}'] = $val;
		}

		// Add special placeholders
		$replace['{post_vars}'] = '$_POST: ' . print_r($_POST, true);
		$replace['{get_vars}']  = '$_GET: ' . print_r($_GET, true);
		$replace['{env}']       = ENVIRONMENT;

		// Allow us to log the file/line that we are logging from
		if (strpos($message, '{file}') !== false)
		{
			list($file, $line) = $this->determineFile();

			$replace['{file}'] = $file;
			$replace['{line}'] = $line;
		}

		// Match up environment variables in {env:foo} tags.
		if (strpos($message, 'env:') !== false)
		{
			preg_match('/env:[^}]+/', $message, $matches);

			if ($matches)
			{
				foreach ($matches as $str)
				{
					$key                 = str_replace('env:', '', $str);
					$replace["{{$str}}"] = $_ENV[$key] ?? 'n/a';
				}
			}
		}

		if (isset($_SESSION))
		{
			$replace['{session_vars}'] = '$_SESSION: ' . print_r($_SESSION, true);
		}

		// interpolate replacement values into the message and return
		return strtr($message, $replace);
	}
protected function interpolate($message, array $context = [])
	{
		if (! is_string($message))
		{
			return $message;
		}

		// build a replacement array with braces around the context keys
		$replace = [];

		foreach ($context as $key => $val)
		{
			// Verify that the 'exception' key is actually an exception
			// or error, both of which implement the 'Throwable' interface.
			if ($key === 'exception' && $val instanceof \Throwable)
			{
				$val = $val->getMessage() . ' ' . $this->cleanFileNames($val->getFile()) . ':' . $val->getLine();
			}

			// todo - sanitize input before writing to file?
			$replace['{' . $key . '}'] = $val;
		}

		// Add special placeholders
		$replace['{post_vars}'] = '$_POST: ' . print_r($_POST, true);
		$replace['{get_vars}']  = '$_GET: ' . print_r($_GET, true);
		$replace['{env}']       = ENVIRONMENT;

		// Allow us to log the file/line that we are logging from
		if (strpos($message, '{file}') !== false)
		{
			list($file, $line) = $this->determineFile();

			$replace['{file}'] = $file;
			$replace['{line}'] = $line;
		}

		// Match up environment variables in {env:foo} tags.
		if (strpos($message, 'env:') !== false)
		{
			preg_match('/env:[^}]+/', $message, $matches);

			if ($matches)
			{
				foreach ($matches as $str)
				{
					$key                 = str_replace('env:', '', $str);
					$replace["{{$str}}"] = $_ENV[$key] ?? 'n/a';
				}
			}
		}

		if (isset($_SESSION))
		{
			$replace['{session_vars}'] = '$_SESSION: ' . print_r($_SESSION, true);
		}

		// interpolate replacement values into the message and return
		return strtr($message, $replace);
	}
Replaces any placeholders in the message with variables
from the context, as well as a few special items like:

{session_vars}
{post_vars}
{get_vars}
{env}
{env:foo}
{file}
{line}

@param mixed   $message
@param array   $context

@return mixed