<script>
  function btn_click() {
    var inout = $("#in").val();
    $("#out").val(inout);
  }
</script>
<form>
  <input type="text" id="in" value="Hello, World!" />
  <input type="button" id="btn" value="→" onClick="btn_click()" />
  <input type="text" id="out" readonly />
  <input type="reset" value="clear" />
</form>

<script>
  function btn2_click() {
    $.post(
      './jquery_01.cgi',
      { 'value' : $('#in2').val() },
      function (data) {
        $('#out2').val( data );
      }
    );
  }
</script>
<form>
  <input type="text" id="in2" value="Hello, World!" />
  <input type="button" id="btn2" value="→" onClick="btn2_click()" />
  <input type="text" id="out2" readonly />
  <input type="reset" value="clear" />
</form>

サーバサイド [ jquery_01.cgi ]

#! /usr/local/bin/ruby
# coding: utf-8

require 'cgi'

cgi = CGI.new
print "Content-type: text/plain; charset=\"utf-8\"\n\n"
print "入力値は" + cgi["value"]