import re
line ="JnJ LLC Invoice# SMT/778"
pattern = re.compile('invoice#\s+([A-Za-z]{3}/\d{1,5})', re.I)
print( re.findall(pattern, line) )
# get the first match
m = pattern.search(line)
if m:
print(m.group(1))
aW1wb3J0IHJlCmxpbmUgPSJKbkogTExDIEludm9pY2UjIFNNVC83NzgiCnBhdHRlcm4gPSByZS5jb21waWxlKCdpbnZvaWNlI1xzKyhbQS1aYS16XXszfS9cZHsxLDV9KScsIHJlLkkpCnByaW50KCByZS5maW5kYWxsKHBhdHRlcm4sIGxpbmUpICkKIyBnZXQgdGhlIGZpcnN0IG1hdGNoCm0gPSBwYXR0ZXJuLnNlYXJjaChsaW5lKQppZiBtOgoJcHJpbnQobS5ncm91cCgxKSk=