Merge a lot of shapefiles with ogr2ogr (in Windows shell)

mergeshape.bat

@echo off
mkdir merged
set counter=0

setlocal ENABLEDELAYEDEXPANSION

for %%f in (*.shp) do (
	if not exist merged\mergedFilter.shp (
		echo Uniendo %%f
		ogr2ogr -f "ESRI Shapefile" merged\mergedFilter.shp %%f
	) else (
		echo Uniendo %%f - Iteracion !counter!
		ogr2ogr -f "ESRI Shapefile" -update -append merged\mergedFilter.shp %%f  
		if !counter! GTR 500 (
			echo Simplificando %%f
			ogr2ogr -f "ESRI Shapefile" merged\mergedFilterAux.shp merged\mergedFilter.shp -sql "SELECT * FROM mergedFilter GROUP BY id_parcela" -dialect sqlite
			del merged\mergedFilter.*
			ren merged\mergedFilterAux.* mergedFilter.*
			set counter=0
		)
	)
	set /A counter=counter+1
)