import sys
f = sys.argv[1]
o = sys.argv[2]
n = sys.argv[3]
with open(f, 'r', encoding='utf-8') as fh:
    c = fh.read()
if o not in c:
    print(f"NOT FOUND: {o[:50]}...")
    sys.exit(1)
c = c.replace(o, n, 1)
with open(f, 'w', encoding='utf-8') as fh:
    fh.write(c)
print(f"OK: patched {f}")