in reply to File name regex

I believe this will do what you ask, where if the option '_nnn' is present then the extension should be '.ilf', or if it is ' nnn' then the extension should be '.sht'; whilst capturing the entire optional part to $1 and the last digit of that optional part to $2:

Update: tightened slightly. Update2: Tightening removed; unnecessary. 

    m[ ^ \d{8} ( (?(?=.* \. ilf) _ | \s | (?!) ) ) (\d)+ )* \. (?:ilf|
+sht) ]x

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Whether you would call that a 'shortcut' is debatable.

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