Class from http://code.tutsplus.com/tutorials/managing-cron-jobs-with-php--net-19428

Ssh2_crontab_manager.class.php

<?php
 
Class Ssh2_crontab_manager {
 
	private $connection;
	private $path;
	private $handle;
	private $cron_file;
 
	function __construct($host=NULL, $port=NULL, $username=NULL, $password=NULL) {
		$path_length     = strrpos(__FILE__, "/");    
		$this->path   = substr(__FILE__, 0, $path_length) . '/';
		$this->handle   = 'crontab.txt';      
		$this->cron_file = "{$this->path}{$this->handle}";
	 
		try
		{
			if (is_null($host) || is_null($port) || is_null($username) || is_null($password)) throw new Exception("Please specify the host, port, username and password!");
			 
			$this->connection = @ssh2_connect($host, $port);
			if ( ! $this->connection) throw new Exception("The SSH2 connection could not be established.");
	 
			$authentication = @ssh2_auth_password($this->connection, $username, $password);
			if ( ! $authentication) throw new Exception("Could not authenticate '{$username}' using password: '{$password}'.");
		}
		catch (Exception $e)
		{
			$this->error_message($e->getMessage());
		}
	}
	 
	public function exec() {
		$argument_count = func_num_args();
	 
		try
		{
			if ( ! $argument_count) throw new Exception("There is nothing to execute, no arguments specified.");
	 
			$arguments = func_get_args();
	 
			$command_string = ($argument_count > 1) ? implode(" && ", $arguments) : $arguments[0];
	 
			$stream = @ssh2_exec($this->connection, $command_string);
			if ( ! $stream) throw new Exception("Unable to execute the specified commands: <br />{$command_string}");
	 
		}
		catch
		{
			$this->error_message($e->getMessage());
		}
	 
		return $this;
	}
	 
	public function write_to_file($path=NULL, $handle=NULL) {
		if ( ! $this->crontab_file_exists())
		{   
			$this->handle = (is_null($handle)) ? $this->handle : $handle;
			$this->path   = (is_null($path))   ? $this->path   : $path;
	 
			$this->cron_file = "{$this->path}{$this->handle}";
	 
			$init_cron = "crontab -l > {$this->cron_file} && [ -f {$this->cron_file} ] || > {$this->cron_file}";
	 
			$this->exec($init_cron);
		}
	 
		return $this;
	}
	 
	public function remove_file() {
		if ($this->crontab_file_exists()) $this->exec("rm {$this->cron_file}");
	 
		return $this;
	}
	 
	public function append_cronjob($cron_jobs=NULL) {
		if (is_null($cron_jobs)) $this->error_message("Nothing to append!  Please specify a cron job or an array of cron jobs.");
		 
		$append_cronfile = "echo '";        
		 
		$append_cronfile .= (is_array($cron_jobs)) ? implode("\n", $cron_jobs) : $cron_jobs;
		 
		$append_cronfile .= "'  >> {$this->cron_file}";
		 
		$install_cron = "crontab {$this->cron_file}";
	 
		$this->write_to_file()->exec($append_cronfile, $install_cron)->remove_file();
		 
		return $this;
	}
	 
	public function remove_cronjob($cron_jobs=NULL) {
		if (is_null($cron_jobs)) $this->error_message("Nothing to remove!  Please specify a cron job or an array of cron jobs.");
		 
		$this->write_to_file();
	 
		$cron_array = file($this->cron_file, FILE_IGNORE_NEW_LINES);
		 
		if (empty($cron_array)) $this->error_message("Nothing to remove!  The cronTab is already empty.");
		 
		$original_count = count($cron_array);
		 
		if (is_array($cron_jobs))
		{
			foreach ($cron_jobs as $cron_regex) $cron_array = preg_grep($cron_regex, $cron_array, PREG_GREP_INVERT);
		}
		else
		{
			$cron_array = preg_grep($cron_jobs, $cron_array, PREG_GREP_INVERT);
		}   
		 
		return ($original_count === count($cron_array)) ? $this->remove_file() : $this->remove_crontab()->append_cronjob($cron_array);
	}

	public function remove_crontab() {
		$this->exec("crontab -r")->remove_file();
		 
		return $this;
	}
	 
	private function crontab_file_exists() {
		return file_exists($this->cron_file);
	}
	 
	private function error_message($error) {
		die("<pre style='color:#EE2711'>ERROR: {$error}</pre>");
	}
 
}

?>