〜だけしか〜ない details

だけしかない

only that much and no more — だけ and しか stacked, so the shortfall is the point

今いま、財布さいふの中なかには切符きっぷだけしかない。

ima, saifu no naka ni wa kippudakeshikanai.

Right now, in my wallet I have only the ticket. neutral

締しめ切きりまで、もう三日みっかだけしかないよ。

shimekiri made, mou mikka dake shika nai yo.

There are only three days left until the deadline. casual

Examples

only N and no more — the amount is named, and the negative predicate paints everything past it as missing

今いま、財布さいふの中なかには切符きっぷだけしかない。

ima, saifu no naka ni wa kippudakeshikanai.

Right now, in my wallet I have only the ticket. neutral

締しめ切きりまで、もう三日みっかだけしかないよ。

shimekiri made, mou mikka dake shika nai yo.

There are only three days left until the deadline. casual

この機械きかいを扱あつかえるのは、社内しゃないに二人ふたりだけしかいません。

kono kikai o atsukaeru no wa, shanai ni futari dake shika imasen.

Only two people in the company can operate this machine. neutral

一度いちどだけしか会あっていないのに、名前なまえを覚おぼえていてくれた。

ichido dake shika atte inai noni, namae o oboete ite kureta.

We had met only once, and yet she had remembered my name. neutral

本日ほんじつは、あと二席にせきだけしかご用意よういできません。

honjitsu wa, ato niseki dake shika go youi dekimasen.

For today we have only two seats left available. formal

The predicate must still be negative — だけ does not rescue しか
(×三日みっかだけしかある).

しか〜ない
しか alone already restricts and is the neutral choice; だけしか stacks two restrictors on one noun for emphasis, which is why it belongs to speech — careful writing treats the doubling as redundant and cuts it back to plain しか.
だけ
One-sided selection — しか cannot appear without a negative predicate while だけ takes either, so だけ states the amount as bookkeeping (五百円ごひゃくえんだけ持もっている) and だけしか forces the negative frame that reads the same amount as a shortfall.

でしかない
Both end in しか〜ない, but でしかない passes a dismissive JUDGEMENT on what something amounts to (言いい訳わけでしかない, "it is nothing but an excuse"), while だけしか〜ない measures a QUANTITY and says how little of it there is.