import re

pattern = r"(?:\b|(?<=_))output(?:\b|(?=_))"
strings = [
    "output",
    "output_of_my_program",
    "my_output_from_program",
    "program_output",
    "my_programoutput"
]

for s in strings:
    m = re.search(pattern, s)
    if m:
        print(f"{s} --> {m.group()}")