Restrish: A restricted shell written in PHP. Allows whitelisting commands.

restrish

#!/usr/bin/env php
<?php

$allow = array('cd', 'ls');
$prompt = 'restrish';
$warning = 'Command not allowed: %s';

/****** TODO LIST
 - Better parsing of command delimiters (ignore quoted delimiters)
 - Use readline for command history
*******/

define('DELIMS', '[;|&><]+');

pcntl_signal(SIGINT, function(){});

function say($str)
{
	fwrite(STDOUT, $str);
}

function prompt($continue = false)
{
	global $prompt;

	say($continue ? ' > ' : $prompt.'$ ');

	return trim(fgets(STDIN));
}

function parts($command)
{
	return preg_split('/('.DELIMS.')/', $command);
}

function allowed($command)
{
	global $allow;

	// Find each command
	$commands = parts($command);
	if (count($commands) > 1)
	{
		foreach ($commands as $command)
		{
			if ( ! allowed(trim($command))) return false;
		}
		return true;
	}

	$path = (strpos($command, ' ') !== false)
		? substr($command, 0, strpos($command, ' '))
		: $command;

	$filename = (strpos($path, '/') !== false)
		? substr($path, strrpos($path, '/'))
		: $path;

	return in_array($filename, $allow);
}

function clean($command)
{
	$exp = '/(?:'.DELIMS.'|^)?\s*(.+?)\s*(?:'.DELIMS.'|$)/';

	return preg_replace_callback($exp, function($matches)
	{
		return escapeshellcmd($matches[0]);
	}, $command);
}

function run($command)
{
	global $warning;

	// Get the base command name
	if ( ! allowed($command))
	{
		throw new Exception(sprintf($warning, $command));
	}

	passthru(clean($command));
}

// Single-command mode
if ($argc > 2 && $argv[1] == '-c')
{
	array_shift($argv);
	array_shift($argv);
	$command = implode(' ', $argv);

	try
	{
		say(run($command));
	}
	catch (Exception $e)
	{
		say($e->getMessage());
		exit(1);
	}
	
	exit(0);
}

// Interactive Mode
while (1)
{
	$command = prompt();

	while (substr($command, -1) == '\\')
	{
		$command = trim(substr($command, 0, strlen($command)-1)).' '.prompt($continue = true);
	}

	if (empty($command)) continue;

	if ($command == 'exit') exit(0);

	try
	{
		run($command);
	}
	catch (Exception $e)
	{
		say($e->getMessage()."\n");
	}
}