import re
regex = r"^(\w+)(?:\/.*)?$"
test_str = ("Foo/Bar\n"
"Foobar")
result = re.sub(regex, r'\1', test_str, 0, re.MULTILINE)
if result:
print (result)
aW1wb3J0IHJlCgpyZWdleCA9IHIiXihcdyspKD86XC8uKik/JCIKdGVzdF9zdHIgPSAoIkZvby9CYXJcbiIKCSJGb29iYXIiKQpyZXN1bHQgPSByZS5zdWIocmVnZXgsIHInXDEnLCB0ZXN0X3N0ciwgMCwgcmUuTVVMVElMSU5FKQoKaWYgcmVzdWx0OgogICAgcHJpbnQgKHJlc3VsdCk=