How to populate Form field

I have an Upload Form where an image is chosen to be uploaded and the code generates a new file name for it, and then moves the file to the uploads/ folder. Upon Submit the link info - to that image displays - (on the next page) - see code below- How can that link info (instead of being displayed) automatically populate a Form field, before the Form gets submitted? Any help will be appreciated.

  
if ($form_submitted == 'yes') {
    $allowedExts = array("gif", "jpeg", "jpg", "png");
    $temp = explode(".", $_FILES["file"]["name"]);
    $extension = strtolower( end($temp) );
    if (  $_FILES["file"]["size"] < 2000000
    && in_array($extension, $allowedExts) )
    {
    if ($_FILES["file"]["error"]!= 0)
    {
    echo "Return Code: " . $_FILES["file"]["error"] . "<br>";
    } else {
    $length = 20;
    $randomString = substr(str_shuffle(md5(time())),0,$length);
    $newfilename = $randomString . "." . $extension;
    move_uploaded_file($_FILES["file"]["tmp_name"], "upload/" . $newfilename );
    $file_location = '<a href="http://www.---.com/upload/' . $newfilename . '">http://www.---.com/upload/' . $newfilename . '</a>';
    echo $file_location;
    }
    } else {
            echo "Invalid upload file";
          }
      $description = $description . " \n " . $newfilename;
        }

PHP:

        
<form enctype="multipart/form-data" action="uploader.php" method="POST">
          <!--<form name="form_upload" action="uploader.php" method="post">-->

            <div id="upload-video">
              <ul>
                <li style="width:240px; text-align:right;"><strong>[var.lang_title]:</strong></li>
                <li style="width:400px; text-align:left;"><input name="title" type="text" class="upload-video-form-input" value="[var.title]" size="38" />
                </li>

                <li style="width:240px; text-align:right;"><strong>[var.lang_description]:</strong></li>
                <li style="width:400px; text-align:left;"><textarea rows="4" name="description" cols="29" class="upload-video-form-input">[var.description]</textarea>
                </li>

                <li style="width:240px; text-align:right;"><strong>[var.lang_tags]:</strong></li>
                <li style="width:400px; text-align:left;"><input name="tags" type="text" class="upload-video-form-input" value="[var.tags]" size="38" />
                </li>

                <li style="width:240px; text-align:right;">&nbsp;</li>
                <li style="width:300px; text-align:left;" class="upload-video-tags">
                [var.lang_enter_tags].<br />
                      [var.lang_enter_tags_description].</li>


                    <li style="width:240px; text-align:right;">
                     <!--<label for="file">Filename:</label>-->
                    <input type="file" name="file" id="file">


                <li style="width:240px; text-align:right;"><strong>[var.lang_select_channel]:</strong></li>
                <li style="width:400px; text-align:left;">
                  <select class="upload-video-form-input" style="width:160px;" size="1" name="channel" onchange="javascript:ahahscript.ahah('[var.base_url]/uploader.php?sub_cat='+ document.form_upload.channel.value, 'sub_change', '', 'GET', '', this);">
                  &nbsp;[var.fields_all;htmlconv=no]</select>&nbsp;([var.lang_select_one])
                </li>

                <li style="width:240px; text-align:right">&nbsp;</li>
                <li style="width:380px" class="font5_14"><strong>[var.lang_sub_categories]</strong></li>

                <li style="width:240px; text-align:right"><strong>[var.lang_sub_cat]:&nbsp;</strong></li>
                <li style="width:400px; text-align:left;" id="sub_change"><select class="upload-video-form-input" style="width:160px;" size="1" name="sub_cat"></select>&nbsp;([var.lang_optional])</li>

                <li style="width:240px; text-align:center">&nbsp;</li>
                <li class="font5_14" style="width:380px;"><strong>[var.lang_optional_info]</strong></li>

                  <li style="width:240px; text-align:right"><strong>[var.lang_location_recorded]:</strong></li>
                  <li style="width:400px; text-align:left;"><input name="location_recorded" type="text" class="upload-video-form-input" value="[var.location_recorded]" size="25" />
                  </li>

                  <li style="width:240px; text-align:right"><strong>[var.lang_allow_comm]:</strong></li>
                  <li style="width:400px; text-align:left;">
                  <select class="upload-video-form-input" size="1" name="allow_comments">
                    <option value="yes" selected="selected">[var.lang_yes]</option>
                    <option value="no">[var.lang_no]</option>
                  </select>
                </li>

                  <li style="width:240px; text-align:right"><strong>[var.lang_allow_embed]:</strong></li>
                  <li style="width:400px; text-align:left;">
                  <select class="upload-video-form-input" size="1" name="allow_embedding">
                    <option value="yes" selected="selected">[var.lang_yes]</option>
                    <option value="no">[var.lang_no]</option>
                  </select>
                </li>

                  <li style="width:240px; text-align:right"><strong>[var.lang_private_pub]:</strong></li>
                  <li style="width:400px; text-align:left;">
                     <select class="upload-video-form-input" size="1" name="public_private">
                       <option value="public" selected="selected">[var.lang_public]</option>
                       <option value="private">[var.lang_private]</option>
                     </select>
                   </li>

                   <li style="width:240px; text-align:right">&nbsp;</li>
                   <li style="width:400px; text-align:left;">
                     <input class="button-form" type="submit" value="Next &gt;&gt;" name="B3" />
                   </li>
                 </ul>
            </div>
            <input class="upload-video-form-input" type="hidden" name="form_submitted" value="yes" />
          </form>
          <div class="clear-fix"></div>
        </div>
      <div class="container-wide-footer"></div>

HTML: