saga_cmd with gdal

johan@cdh7:/tmp$ saga_cmd shapes_polygons 2 -POLYGONS:/usr/share/qgis/python/plugins/processing/tests/data/polygons.geojson -OUTPUT:out.shp
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   #####   ##   #####    ##
  ###     ###  ##       ###
   ###   # ## ##  #### # ##
    ### ##### ##    # #####
 ##### #   ##  ##### #   ##
____________________________

SAGA Version: 2.2.8

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library path: /usr/lib/x86_64-linux-gnu/saga/
library name: libshapes_polygons
library     : Polygons
tool        : Polygon Properties
author      : V.Olaya (c) 2004, O.Conrad (c) 2011
processors  : 4 [4]
____________________________

ERROR 4: `/usr/share/qgis/python/plugins/processing/tests/data/polygons.geojson' not recognised as a supported file format.



Parameters


Polygons: polygons
Polygons with Property Attributes: Polygons with Property Attributes
Number of Parts: no
Number of Vertices: no
Perimeter: yes
Area: yes


 51%
 51%Save shapes: out.shp...

 51%
 51%okay
johan@cdh7:/tmp$ dbview out.dbf
Id         : 1
Poly num a : 1.1000000000e+00
Poly st a  : string a
Perimeter  : 2.3268682079e+02
Area       : 3.5437191539e+03

Id         : 2
Poly num a : 2.2000000000e+00
Poly st a  : string b
Perimeter  : 2.5424613794e+02
Area       : 4.1141146136e+03