Creating zip or tar.gz archive without exec

If you want to create tar.gz and you are using PHP 5.3+, you can use PharData class:

try
{
    $a = new PharData('archive.tar');

    // ADD FILES TO archive.tar FILE
    $a->addFile('data.xls');
    $a->addFile('index.php');

    // COMPRESS archive.tar FILE. COMPRESSED FILE WILL BE archive.tar.gz
    $a->compress(Phar::GZ);

    // NOTE THAT BOTH FILES WILL EXISTS. SO IF YOU WANT YOU CAN UNLINK archive.tar
    unlink('archive.tar');
} 
catch (Exception $e) 
{
    echo "Exception : " . $e;
}

You can also use PHP compression stream wrappers to compress and uncompress files in one line:

// Reads file.txt, passes it throyuh the zlib wrapper and writes the archive file.txt.gz
copy('data.xls', 'compress.zlib://' . 'data.xls.gz');

// Reads the archive file.txt.gz using zlib wrapper, writes uncompressed file
copy('compress.zlib://' . 'data.xls.gz', 'data.xls');