If you installed qgis with OSGeo setup you have access to a shell which can run directly gdal/ogr. to run a clic processing use this command   ogr2ogr -clipsrc clip_polygon.shp output.shp input.shp replace output and input with your files name

On windows environnement, if you installed Qgis with OSGeoW setup you have access to a shell which can run directly gdal/ogr. to run a clic processing use this command 
ogr2ogr -clipsrc clip_polygon.shp output.shp input.shp
replace output and input with your files name and their path.
If you need more details about OSGEOW have a look to this page

If you installed qgis with OSGeo setup you have access to a shell which can run directly gdal/ogr. to run a clic processing use this command ogr2ogr -clipsrc clip_polygon.shp output.shp input.shp

If you installed qgis with OSGeo setup you have access to a shell which can run directly gdal/ogr. to run a clic processing use this command ogr2ogr -clipsrc clip_polygon.shp output.shp input.shp replace output and input with your files name