将表单字段值传递给PHP文件

I'd like to do a dynamic search function using jQuery and PHP. I'm struggling passing the HTML form field to the JQUERY function (which would then get passed to the PHP file).

My major questions are:

1) How do I pass form "Input" field into Jquery function?

2) How do I get the PHP result in the form "Output" field?

I currently have... (simplified)

JQUERY:
$.get("SEARCH.php", {"_input" :  $('input[name=input]').val()},
function(returned_data) 
{
   $("input[name=output]").val(returned_data);
}


SEARCH.php:
$input = 'Welcome ' . $_GET['_input'];
echo $input;
//should be "Welcome" plus whatever I type in to "input"



HTML FORM:
input: <input type="text" name="input" value="" /> 
output: <input type="text" name="output" id="output" />         

Thank you!

jQuery

$.get("SEARCH.php", {"_input" : $('input[name=input]').val() },
function(returned_data) {
   $("input[name=output]").val( returned_data );
}

HTML

input: <input type="text" name="input" value="" />
output: <input type="text" name="output" />

PHP Use echo instead of return since it looks that your code isn't in function:

$input = $_GET['_input'];
do some parsing of the input
echo $result;

jQuery

$.get("SEARCH.php", {"_input" : $('input[name=input]').val() },
function(returned_data) {
    $('#output').val(returned_data);
});

PHP

$input = $_GET['_input'];
do some parsing of the input
echo $result; // not return

HTML

input: <input type="text" name="input" value="" />
output: <input type="text" name="result" id="output" value="" />