From : http://www.stephenradford.me/blog/tutorials/deploy-via-bitbucket-or-github-service-hooks

deploy.php

<?php

// Set these dependant on your BB credentials

$username = 'username';
$password = 'password';

$branch = 'master';

// FTP Credentials

$ftp_host = 'example.com';
$ftp_username = 'username';
$ftp_password = 'password';
$ftp_path = '/public_html/directory/';

// Grab the data from BB's POST service and decode
$json = stripslashes($_POST['payload']);
$data = json_decode($json);

// Set some parameters to fetch the correct files

$uri = $data->repository->absolute_url;
$node = $data->commits[0]->node;
$files = $data->commits[0]->files;

if($data->commits[0]->branch == $branch){

  $author = $data->commits[0]->author;
	$comm_msg = $data->commits[0]->message;

	$log = "\n\n------NEW COMMIT------\n\nAuthor: $author\nMessage: $comm_msg\n\n";

	$fp = fopen('deploy_log', 'a');
	fwrite($fp, $log);
	fclose($fp);

	// Connect to FTP

	$conn_id = ftp_connect($ftp_host);
	$login_result = ftp_login($conn_id, $ftp_username, $ftp_password);

	// We're gonna need these later!

	function make_directory($ftp_stream, $dir){
		if (ftp_is_dir($ftp_stream, $dir) || @ftp_mkdir($ftp_stream, $dir)) return true;
		if (!make_directory($ftp_stream, dirname($dir))) return false;
		return ftp_mkdir($ftp_stream, $dir);
	}

	function ftp_is_dir($ftp_stream, $dir){
		$original_directory = ftp_pwd($ftp_stream);
		if ( @ftp_chdir( $ftp_stream, $dir ) ) {
			ftp_chdir( $ftp_stream, $original_directory );
			return true;
		} else {
			return false;
		}
	}

	// Foreach through the files and curl them over

	foreach ($files as $file) {

		$logmsg = '';

		$path = $file->file;

		if ($file->type == "removed") {
		
			ftp_delete($conn_id, $ftp_path.$path);
			
			$logmsg .= "[".date('d-m-Y h:i:s')."] - Removed $path\n";
			
		} else {

			$url = "https://api.bitbucket.org/1.0/repositories".$uri."raw/".$node."/".$file->file;
		
			$dirname = dirname($path);

			$chdir = @ftp_chdir($conn_id, $ftp_path.$dirname);
			
			if($chdir == false){
				if(make_directory($conn_id, $ftp_path.$dirname)){
					$logmsg .= "[".date('d-m-Y h:i:s')."] - Created new directory '$dirname'\n";
				} else {
					$logmsg .= "[".date('d-m-Y h:i:s')."] - Failed to create directory '$dirname'\n";
				}
			}
		
			$ch = curl_init($url);
			curl_setopt($ch, CURLOPT_USERPWD, "$username:$password");
			curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
			curl_setopt($ch, CURLOPT_FOLLOWLOCATION, false);
		
			$data = curl_exec($ch);
		
			curl_close($ch);
			
			$temp = tmpfile();
			fwrite($temp, $data);		
			fseek($temp, 0);
			
			ftp_fput($conn_id, $ftp_path.$path, $temp, FTP_BINARY);
			
			fclose($temp);
			
			$logmsg .= "[".date('d-m-Y h:i:s')."] - Uploaded $path\n";
		
		}
		
		$log = "$logmsg";
		
		$fp = fopen('deploy_log', 'a');
		fwrite($fp, $log);
		fclose($fp);
		
	}

	ftp_close($conn_id);

	$log = "\n\n------END COMMIT------\n\n";

	$fp = fopen('deploy_log', 'a');
	fwrite($fp, $log);
	fclose($fp);

}

Hi,
It may be helpful to add this at the beginning of the file :

// Logs
function log_error( $num, $str, $file, $line, $context = null )
{
    $fp = fopen('deploy_log', 'a');
    fwrite($fp, "Error $num : $str at line $line\n");
    fclose($fp);
}
set_error_handler('log_error');