〜しかない

もうやるしかありません。

Mō yaru shika arimasen.

There is nothing for it but to do it.

しかない is no other option, with resignation in it

終電がないので、歩いて帰るしかない。

Shūden ga nai node, aruite kaeru shika nai.

The last train has gone, so it is walking home.

The dead end is usually spelled out first

名詞に付くと「それだけ」の意味になります。

Meishi ni tsuku to sore dake no imi ni narimasu.

On a noun it means only that.

水しかない means only water is there — not that you must drink water