gsub!

/*
 *  call-seq:
 *     gsub!(pattern, replacement)    => string or nil
 *     gsub!(pattern) {|...| block }  => string or nil
 *  
 *  Equivalent to <code>Kernel::gsub</code>, except <code>nil</code> is
 *  returned if <code>$_</code> is not modified.
 *     
 *     $_ = "quick brown fox"
 *     gsub! /cat/, '*'   #=> nil
 *     $_                 #=> "quick brown fox"
 */

static VALUE
rb_f_gsub_bang(argc, argv)
    int argc;
    VALUE *argv;
{
    return rb_str_gsub_bang(argc, argv, uscore_get());
}