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.. _scripting-user:
*********
Scripting
*********
The behavior of FRR may be extended or customized using its built-in scripting
capabilities. The scripting language is Lua 5.3. This guide assumes Lua
knowledge. For more information on Lua, consult the Lua 5.3 reference manual, or
*Programming in Lua* (note that the free version covers only Lua 5.0).
https://www.lua.org/manual/5.3/
http://www.lua.org/pil/contents.html
Scripting
=========
.. seealso:: Developer docs for scripting
How to use
----------
1. Identify the Lua function name. See :ref:`lua-hook-calls`.
2. Write the Lua script
3. Configure FRR to use the Lua script
In order to use scripting, FRR must be built with ``--enable-scripting``.
.. note::
Scripts are typically loaded just-in-time. This means you can change the
contents of a script that is in use without restarting FRR. Not all
scripting locations may behave this way; refer to the documentation for the
particular location.
Example: on_rib_process_dplane_results
--------------------------------------
This example shows how to write a Lua script that logs changes when a route is
added.
First, identify the Lua hook call to attach a Lua function to: this will be the
name of the Lua function. In this case, since the hook call is
`on_rib_process_dplane_results`:
.. code-block:: lua
function on_rib_process_dplane_results(ctx)
log.info(ctx.rinfo.zd_dest.network)
return {}
The documentation for :ref:`on-rib-process-dplane-results` tells us its
arguments. Here, the destination prefix for a route is being logged out.
Scripts live in :file:`/etc/frr/scripts/` by default. This is configurable at
compile time via ``--with-scriptdir``. It may be overridden at runtime with the
``--scriptdir`` daemon option.
The documentation for :ref:`on-rib-process-dplane-results` indicates that the
``script`` command should be used to set the script. Assuming that the above
function was created in :file:`/etc/frr/scripts/my_dplane_script.lua`, the
following vtysh command sets the script for the hook call:
.. code-block:: console
script on_rib_process_dplane_results my_dplane_script
After the script is set, when the hook call is hit, FRR will look for a
*on_rib_process_dplane_results* function in
:file:`/etc/frr/scripts/my_dplane_script.lua` and run it with the ``ctx`` object
as its argument.
.. _lua-hook-calls:
Available Lua hook calls
========================
:ref:`on-rib-process-dplane-results`
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