gzwrite() writes the contents of string to the given gz-file.
The gz-file pointer. It must be valid, and must point to a file successfully opened by gzopen().
The string to write.
The number of uncompressed bytes to write. If supplied, writing will stop after length (uncompressed) bytes have been written or the end of string is reached, whichever comes first.
Note that if the length argument is given, then the magic_quotes_runtime configuration option will be ignored and no slashes will be stripped from string.
$string = 'Some information to compress';
$gz = gzopen('somefile.gz','w9');