- What is the halacha regarding opening soda cans on shabbos?
First and foremost in order to satisfy the opinions of all the poskim, it is recommended that all bottles and containers be opened before Shabbos.
Rav Moshe Feinstein says one should not open cans even though people throw them out and hence do not create a Kli (vessel) .This is because people don't grasp the distinction between the status of cans that may be opened and those that may not. He brings the Gemara Shabbat (Daf,139) where the Gemara forbids certain permissible activities for communities where the people aren't learned as a reason for this prohibition. Rav Moshe quotes the prevalence of Chillul Shabbat in our generation as a reason for refraining from issuing a lenient ruling which will lead to more Chillul Shabbas.However, in the case of someone who made a sheva berachos or who invited guests and finds, to his embarrassment, that he does not have enough food to serve, he permits having a gentile open the cans and other containers on Shabbos (Shu”t Igros Moshe 1:122; for a similar approach, see Shu”t Chelkas Yaakov 3:8).
Chazon Ish,says that opening a can is creating a Kli, and therefore one should not open cans as the person violates a Torah prohibition of creating Kelim (Orach Chayim 51:13).
Rav Shlomo Zalman Auerbach(Shmiras Shabbat Kehilchata 9: footnote 10) Rav Ovadia Yosef (Teshuvot Yechave Daat 2:42) Both allow opening cans on Shabbos since cans are thrown out after use.But even they do not allow opening of a can if he intends to use it afterwards.
2.Can I ask a person to open it for me?
Even someone who does not open cans on Shabbos may use a can that was opened on Shabbos even if they were opened for him (Iggres Moshe: O"C Chelek Daled Siman Kuf Yud Tes Ois Heh) and does not require the person who opened it to drink from it. Non the less he may not ask someone to open it for him(Kuntres Yad Dodi, Harav Dovid Feinstein,pg. 31).