import os

files_list = []
for dirpath, dirnames, filenames in os.walk("/home/murat/Desktop/grass-6.2.1"):
    for file in filenames:
        files_list.append( os.path.join(dirpath, file))

for x in files_list:
    os.system("sed 's/GRASS_XTERM/GRASS_KONSOLE/g' %s" % x)