if (it) doesn't exist; if there is no ...; if (one) doesn't have ...
if not ...; unless ...
have to ...; must ...
早く寝なきゃ明日起きられない。
I have to go to bed early or I won't be able to get up tomorrow.
この書類は今日中に出さなきゃ。
I have to submit this document by today.
努力しなきゃ結果は出ないよ。
You won't get results if you don't make an effort.