import re
pattern = r"^[a-f\d]+(?:-{1,2}>[a-f\d]+)+$"
s = ("0912adbd->12d1829-->218990d\n"
"ab2c8d-->82a921->193acd7\n"
"test")
print(re.findall(pattern, s, re.I | re.M))
aW1wb3J0IHJlCgpwYXR0ZXJuID0gciJeW2EtZlxkXSsoPzotezEsMn0+W2EtZlxkXSspKyQiCnMgPSAoIjA5MTJhZGJkLT4xMmQxODI5LS0+MjE4OTkwZFxuIgogICAgICAgICAgICAiYWIyYzhkLS0+ODJhOTIxLT4xOTNhY2Q3XG4iCiAgICAgICAgICAgICJ0ZXN0IikKcHJpbnQocmUuZmluZGFsbChwYXR0ZXJuLCBzLCByZS5JIHwgcmUuTSkp