Outputting XML to file - sql

Question

I am brand new to XML as well as SQL procedures, and I am trying to get this to output to a .txt (or .xml?) on one of our UNIX server. I have been looking at various things online, but having trouble getting it right. Could someone push me in the right direction?
create or replace procedure markviewimport_interface (p_invoice_id number(10), p_filename nvarchar(30))
is
v_output clob;
begin
SELECT
XMLFOREST(
XMLCONCAT(
XMLELEMENT("CREATEDBY",XMLATTRIBUTES('Exported By' AS "header"), 'Magellan IT'),
XMLELEMENT("TIMESTAMP",XMLATTRIBUTES('Date' AS "header"), TO_CHAR(SYSDATE,'MM.DD.YYYY')),
XMLFOREST(
XMLFOREST(
XMLFOREST(
'invoice_id' AS "DBFIELD",
'Invoice ID' AS "CAPTION",
r_markviewimport.invoice_id AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'vendor_num' AS "DBFIELD",
'Vendor Num' AS "CAPTION",
r_markviewimport.vendor_num AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'vendor_name' AS "DBFIELD",
'Vendor Name' AS "CAPTION",
r_markviewimport.vendor_name AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'po_number' AS "DBFIELD",
'PO Number' AS "CAPTION",
r_markviewimport.po_number AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'invoice_date' AS "DBFIELD",
'Invoice Date' AS "CAPTION",
r_markviewimport.invoice_date AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'invoice_num' AS "DBFIELD",
'Invoice Number' AS "CAPTION",
r_markviewimport.invoice_num AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'terms_name' AS "DBFIELD",
'Terms Date' AS "CAPTION",
r_markviewimport.terms_name AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'invoice_amount' AS "DBFIELD",
'Invoice Amount' AS "CAPTION",
r_markviewimport.invoice_amount AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'amount_applicable_to_discount' AS "DBFIELD",
'Amount Applicable to Discount' AS "CAPTION",
r_markviewimport.amount_applicable_to_discount AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'amount_paid' AS "DBFIELD",
'Amount Paid' AS "CAPTION",
r_markviewimport.amount_paid AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'payment_date' AS "DBFIELD",
'Payment Date' AS "CAPTION",
r_markviewimport.payment_date AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'filename' AS "DBFIELD",
'File Name' AS "CAPTION",
r_markviewimport.filename AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'complete_filename' AS "DBFIELD",
'Complete File Name' AS "CAPTION",
r_markviewimport.complete_filename AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'document_id' AS "DBFIELD",
'Document ID' AS "CAPTION",
r_markviewimport.document_id AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'text' AS "DBFIELD",
'Text' AS "CAPTION",
r_markviewimport.text AS "VALUE"
) AS "DATA_ITEM",
XMLFOREST(
'tool_name' AS "DBFIELD",
'Tool Name' AS "CAPTION",
r_markviewimport.tool_name AS "VALUE"
) AS "DATA_ITEM"
) AS "BASICDATA"
)
) AS "DATA_ROOT"
) .getclobval() into v_output
FROM
(
SELECT DISTINCT inv.invoice_id,
vendor.segment1 vendor_num,
vendor.vendor_name,
poh.segment1 po_number,
inv.invoice_date,
inv.invoice_num,
terms.name terms_name,
inv.invoice_amount,
inv.amount_applicable_to_discount,
inv.amount_paid,
pmt.check_date payment_date,
path.filename,
path.complete_filename,
path.document_id,
stamps.text,
stamps.tool_name
FROM apps.ap_invoices_all inv,
apps.ap_invoice_distributions_all dist,
apps.po_distributions_all podi,
apps.ap_invoice_payment_history_v pmt,
apps.fnd_attached_docs_form_vl fnd,
markview.mv_page_image_paths path,
apps.po_vendors vendor,
apps.po_headers_all poh,
apps.ap_terms terms,
(
SELECT mp.document_id,
moi.markup_object_id,
moi.page_markups_view_id,
moi.text,
mvt.tool_name,
mp.page_id
FROM markview.mv_markup_object moi,
markview.mv_tool mvt,
markview.mv_page_markups_view mpmv,
markview.mv_page mp
WHERE moi.tool_id = mvt.tool_id
AND mp.page_id = mpmv.page_id
AND mpmv.page_markups_view_id = moi.page_markups_view_id
AND mvt.tool_id IN
(
SELECT mvt.tool_id
FROM markview.mv_tool
WHERE mvt.tool_name IN ( 'Green Text',
'Blue Sticky Note' ) )) stamps
WHERE inv.invoice_id = to_number(fnd.pk1_value)
AND inv.invoice_id = dist.invoice_id
AND poh.po_header_id(+) = podi.po_header_id
AND podi.po_distribution_id(+) = dist.po_distribution_id
AND fnd.file_name = to_char(path.document_id)
AND inv.invoice_id = pmt.invoice_id
AND path.document_id = stamps.document_id(+)
AND path.page_id = stamps.page_id(+)
AND fnd.category_description = 'MarkView Document'
AND fnd.entity_name = 'AP_INVOICES'
AND inv.vendor_id = poh.vendor_id(+)
AND inv.terms_id = terms.term_id
AND inv.vendor_id = vendor.vendor_id
AND path.platform_name = 'UNIX_FS_TO_DOC_SERVER'
AND pmt.void = 'N'
--AND inv.invoice_id = 4796324
DBMS_XSLPROCESSOR.clob2file(v_output, 'My Directory', 'output.xml');
) r_markviewimport
Here is my procedure, where am I going wrong?
Thanks!