import glob
import fileinput
import sys

if len(sys.argv) != 4:
    print("Usage: python3 replace.py [files_pattern] [old_string] [new_string]")
    sys.exit(1)

pattern = sys.argv[1]
old_string = sys.argv[2]
new_string = sys.argv[3]

for file in glob.glob(pattern):
    with fileinput.FileInput(file, inplace=True) as f:
        for line in f:
            print(line.replace(old_string, new_string), end='')