Merge shapefiles in folders and subfolders with arcpy

I try to merge 20 shapefiles in order to get one shapefile that include all the features. All shapefiles are called "migrashim", and they spread in big folder that divided to a lot of sub folders. My code is:

import arcpy,os,sys,string,fnmatch
import arcpy.mapping
from arcpy import env

rootPath = 'C:\Project\layers'
pattern = 'migrashim.shp'
counter = 0
for root, dirs, files in os.walk(rootPath):
    for filename in fnmatch.filter(files, pattern):

        print( os.path.join(root, filename))
        arcpy.Merge_management(["migrashim.shp"], r"C:\Project\layers\migrashim_total.shp")
        counter = counter + 1
print counter

and i get an error:

ERROR 000732: Input Datasets: Dataset migrashim.shp does not exist or is not supported Failed to execute (Merge).

Answer

So currently you're using the input of your shape file name but not indicating a directory. The full path is needed for the merge to work. Or you can set your environment's workspace each time you find a file. You're also not actually merging anything, since you have only a single input.

I'd populate a list of all the matches found, so that you can use it to perform a single merge at the end of your code.

Try something like this:

matches = []

for root, dirs, files in os.walk(rootPath):
    for filename in files:
        if filename == "migrashim.shp":
            match = ( os.path.join(root, filename))
            matches.append (match)

            counter = counter + 1

arcpy.Merge_management(matches, r"C:\Project\layers\migrashim_total.shp")