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