将PHP请求发送到文本文件

What I want is to call for instance /?Hello and then the PHP program to upload "Hello" to the textfile.

<?php 
    $sqldata = array (serialize($_REQUEST), $_SERVER['PHP_AUTH_USER']);
    file_put_contents('textfile.txt', $sqldata); 
?>

If this is called, it comes out like this:

a:7:
{
    s:4:"Hello";
    s:0:"";
    s:8:"__cfduid";
    s:43:"d1e090c0f439f6aa6bad2e7b18dd9dc701473462630";
    s:9:"PHPSESSID";
    s:32:"6d602111da31b9a1646fa11d3c3c7e72";
    s:8:"cvo_sid1";s:12:"KTVET3PF62UB";
    s:9:"utag_main";
    s:197:"v_id:0157856889ad001e67d2f49d3db10206d006e06500918$_sn:1$_ss:0$_pn:2;exp-session$_st:1475413904309$ses_id:1475412003245;exp-session$dc_visit:1$dc_event:2;exp-session$dc_region:eu-west-1;exp-session";
    s:8:"cvo_tid1";
    s:38:"Bkbwvk_D0Uc|1475412341|1475412443|-337";
    s:12:"cf_clearance";
    s:60:"20d986c985fb1cbab15f286ed34cc09d79c7fb06-1475683723-31536000";
}

I then tried this, hoping it would take out only the part that says "Hello"

<?php 
    $sqldata = array (serialize($_REQUEST), $_SERVER['PHP_AUTH_USER']);
    $myarray[array ]['4'];
    file_put_contents('textfile.txt', $myarray); 
?>

My end objective, is to request something just like /?Hello and have just that uploaded to the text file.

What you are doing when you request a page with just ?Hello is actually setting the key "Hello" without a content, which would be the same as ?Hello=

You can test for this by using the following code:

<?php
if ( isset($_REQUEST['Hello']) ) {
    // Write stuff to the file.
}

If you don't want it to be triggered when a POST variable Hello is present, change the $_REQUEST to a $_GET

I am assuming that you do not know the exact key in advance and "Hello" can actually be anything.

In that case, you can use array_keys() to access keys of any array. So in this case, you want to access keys of $_GET. so something like:

$arrKeys = array_keys($_GET)

will give you all the keys. You can then save them to a file.