import re
s = "aba\naaa\naba\naaa\naba"
print( "\n".join([st for st in s.splitlines() if 'b' not in st]) )
print("---")
print( re.sub(r'^[^b\r\n]*b.*[\r\n]*', '', s, flags=re.M) )
print("---")
aW1wb3J0IHJlCnMgPSAiYWJhXG5hYWFcbmFiYVxuYWFhXG5hYmEiCnByaW50KCAiXG4iLmpvaW4oW3N0IGZvciBzdCBpbiBzLnNwbGl0bGluZXMoKSBpZiAnYicgbm90IGluIHN0XSkgKQpwcmludCgiLS0tIikKcHJpbnQoIHJlLnN1YihyJ15bXmJcclxuXSpiLipbXHJcbl0qJywgJycsIHMsIGZsYWdzPXJlLk0pICkKcHJpbnQoIi0tLSIpCg==