Gemara

(Rav Huna): If an herb was inserted into moist earth, it is permitted [to remove it and re-insert it on Shabbos] only if he removed and re-inserted it before Shabbos.

(Shmuel): If a knife was inserted between rows of bricks in a wall, it is permitted only if he removed and re-inserted it before Shabbos.

Question (Rav Ketina - Mishnah): If one buried turnips or radishes under a vine, leaving some of the leaves exposed, one may remove them on Shabbos.

This is a refutation.

102b (Rav): If one makes a hole in a chicken coop, he is liable for building;

(Shmuel): He is liable for Makeh b'Patish.

146a (Rabah): Mid'Oraisa, one is not liable for a hole unless it is made for entrance and exit;

Chachamim decreed to forbid due to a hole in a chicken coop, which lets in air and lets out heat.

(Beraisa): One may widen a hole.

We are not concerned lest he widen a hole in a chicken coop. He would not, lest a Sheretz enter [and kill chickens].

(Beraisa): Some forbid widening.

Sometimes it was made too small, and he needs to widen it.

(Rav Nachman): The Halachah follows the opinion that forbids.

(Beraisa): All permit opening an old hole that was sealed.

Rishonim

Rambam (Hilchos Shabbos 23:1): If one makes a hole for entrance and exit, e.g. in a chicken coop, he is liable for Makeh b'Patish. Chachamim decreed to forbid any hole, even only for exit or only for entrance. Therefore, one may not make a new hole in a barrel or add to a hole. However, one may open an old hole.

Mordechai (440): The Gemara discusses one who intends to widen the hole. However, if a knife was inserted in a barrel from before Shabbos, he may remove it and return it, for he does not intend to widen. Shmuel taught that if a knife was inserted between rows of bricks in a wall, removed and re-inserted before Shabbos, it is permitted on Shabbos. All permit re-opening an old hole. We must say that this is even with a drill, e.g. if the spigot broke. We do not distinguish between a big and small hole. One should not be so stringent, for it is considered a hole only if it is made for entrance and exit. Rabanan decreed due to a chicken coop. Therefore, we permit [re-opening] an old hole.

Terumas ha'Deshen (64): If a knife was inserted in a wall, we must be concerned if he removes it. One is liable for drilling any amount. We hold like Rav, who obligates due to Binyan. This is even before it is filled in. If a knife was inserted somewhat forcefully, it is almost a Pesik Reishei that it will increase the hole. This is like drilling a little. Do not bring a proof to permit from the Mordechai, who permits removing a knife that was inserted in a barrel and returning it, since he does not intend to widen. He brings a proof from a knife inserted between rows of bricks that was removed and re-inserted before Shabbos. The Mordechai permitted regarding a barrel. All agree that Binyan and Stirah do not apply to Kelim, unless they strengthen it or require a professional. Drilling does not apply, even if it were a Pesik Reishei that it will increase the hole. He is not liable for increasing the hole, since it is not made for entrance and exit. Chachamim decreed due to a chicken coop. They forbade one who intends to widen. We can permit one who does not intend, even if it is a Pesik Reishei, since it is mid'Rabanan. The Mordechai says so in the name of Maharam. However, it seems that the Mordechai permits a knife that was removed and re-inserted before Shabbos, which is not a Pesik Reishei to widen the hole, for he learns from such a case, i.e. the knife between rows of bricks. Therefore, it is permitted even for a barrel that holds 40 Sa'im. Or Zaru'a says that Binyan applies to big Kelim. If it were a Pesik Reishei that he will widen the hole, he would be liable. One cannot be liable for a knife between bricks. Drilling does not apply, for it is not one entity. He merely separates the bricks. The custom is not to remove a knife from a wall. I justified this. It is good to justify a custom to be lenient, and all the more so a custom to be stringent. However, there is no reason to be stringent about a knife in a barrel.

Poskim

Shulchan Aruch (OC 314:1): One may not widen an opening in a Kli.

Taz (2): It seems that the Shulchan Aruch, Tur and Mordechai permit even if it is a Pesik Reishei, as long as he does not intend to widen. The Mordechai learned from Shmuel. It seems that the Mordechai permits only a similar case, when he removed it before Shabbos. This is difficult, for the Gemara refuted Shmuel and Rav Huna! The Beis Yosef says that he learns from the conclusion, which permits even if it was not removed and re-inserted before Shabbos. We permit because he does not intend. The words [of the Mordechai] connote unlike this. Also, the Mordechai should have learned from the Mishnah of burying a turnip, which explicitly permits. Why does he learn from Shmuel, who is more stringent than the Mishnah?

Taz (2): Rather, the Mordechai explains Rav Huna and Shmuel like Tosfos (Reish 44a), that the concern is moving earth and widening the hole. When the turnip was buried, it sealed the hole. If he removed it before Shabbos, there was a proper hole. He re-inserted before Shabbos. When he removes it on Shabbos, he slightly widens the hole, just like on 146a. Even so, it is permitted because he does not intend to add. We challenged Rav Huna and Shmuel, because the Mishnah does not stipulate that it was removed before Shabbos! It seems that it permits due to Melachah she'Einah Tzerichah l'Gufah (Beitzah 8a). This is forbidden mid'Rabanan, but Chachamim permitted for Simchas Yom Tov regarding a shovel inserted in earth (Tosfos). On Shabbos it is forbidden, i.e. when it is Nicha Lei (he desires this). Even if he does not want the hole, he wants the earth. Regarding the turnip, he wants only the turnip, but not the earth. Therefore it is permitted even if he did not remove and re-insert it before Shabbos. This refutes Rav Huna and Shmuel. The Mordechai learns from Rav Huna and Shmuel. Even though they forbid making a hole, they permit through removal and re-insertion before Shabbos. The same applies to removing a knife from a barrel. We cannot bring a proof from the Mishnah. There, there is no Isur to make the hole. It is Asur to make a new hole in a barrel. This is only for a matter in which there is no Isur Torah for one who intends.

Taz (2): The Terumas ha'Deshen discusses one who inserted a knife before Shabbos in order to remove wine from the barrel. If he removes it for the first time on Shabbos, this completes the hole. It is only mid'Rabanan, for he will not enter anything through the hole. How did the Terumas ha'Deshen learn from Shmuel, who was refuted? Also, why does he equate removing a knife from a wall to drilling? He does not need the hole! Rather, my explanation of the Mordechai is clear, unlike the Terumas ha'Deshen. If so, even if a knife was inserted in a wall before Shabbos, one may remove it for the first time on Shabbos. However, I cannot be lenient against Terumas ha'Deshen, the Mechaber and Rema (Sa'if 12).

Taz (2) and Mishnah Berurah (11): Regarding a knife in a barrel, the Mechaber rules unlike the Terumas ha'Deshen and Rema. For a great need, one may rely on them.

Mishnah Berurah (9): Even if he does not make it big enough for entrance and exit, it is forbidden mid'Rabanan.

Rema: It is forbidden only if he intends for this.

Mishnah Berurah (10): The Rema explains the Mechaber, who forbids only if he intends. The Rema himself (below) forbids even without intent if it is a Pesik Reishei.

Shulchan Aruch (ibid.): If a knife was inserted from before Shabbos, he may remove it and return it, for he does not intend to widen.

Beis Yosef (DH v'Afilu): Based on what I wrote below, even if he did not remove and re-insert it before Shabbos, it is permitted.

Gra (DH v'Im, according to Damesek Eliezer): The Terumas ha'Deshen learned about removing a knife from a barrel, from a knife between rows of bricks. He explains like Tosfos, that the issue was moving earth, but not widening the hole. We must say that the case is that he does not widen it. We conclude that it is permitted even if he did not remove and re-insert it before Shabbos , for it is Tiltul Min ha'Tzad for the sake of Heter. The Beis Yosef explains that the Terumas ha'Deshen held that only Rav Huna was refuted, but not Shmuel. This is unlike the Rif and Rambam; in the Shulchan Aruch, he rules like them. Really, the Terumas ha'Deshen agrees that Shmuel was refuted. The Magen Avraham (below) is correct. One may remove the knife, for he does not need the hole and it is Mekalkel.

Rema: If he did not remove it at least once before Shabbos, it is forbidden, for it is a Pesik Reishei of making an opening in a barrel.

Magen Avraham (5): All forbid a Pesik Reishei. We must say that Shmuel discusses when it is not a Pesik Reishei, and also 146a discusses this. Making a hole in a barrel is a Torah Isur. The Terumas ha'Deshen brings from the Mordechai to permit a Pesik Reishei for mid'Rabanan laws. We say that making holes is not a reason to forbid moving pillars (Shabbos 113a). We learn from the turnip, even though it is a Pesik Reishei! Rather, it is permitted because it is Mekalkel. Letter of the law, one may remove a knife even from a wall or a big barrel, for it is Eino Miskaven and Mekalkel. The Terumas ha'Deshen came to justify the custom to be stringent.

Kaf ha'Chayim (14): For an Isur mid'Rabanan, the Magen Avraham, Eliyahu Rabah, Gra and R. Akiva Eiger forbid a Pesik Reishei d'Nicha Lei without intent. However, here the Magen Avraham and Gra permit even regarding a wall, for it is Mekalkel. The Taz held like this, but was wary to rule against the Shulchan Aruch. The primary opinion permits, but where there is not such a need, one should be stringent.

Gra (DH d'Oseh): The Beis Yosef asked why the Terumas ha'Deshen does not require that something detached was removed and re-inserted, but he requires this for a barrel. The Darchei Moshe answered that here he makes an opening.

Mishnah Berurah (11,12): In Sa'if 12, we permit removing a knife from something detached, even if it was not removed before Shabbos. Here is more stringent, for he fixes the opening. Even if the opening is not needed for entrance and exit, this is forbidden mid'Rabanan. For a big need, one may be lenient.