Tearing Toilet Paper on Shabbat
It is forbidden to rip toilet paper on Shabbat, and doing so may be a violation of several melachot. This is true whether one cuts the toilet paper along the perforated lines or in between them. Most authorities classify tearing toilet paper (or attached tissues) under the melachot of koraya (tearing), mechatech (measured cutting), and/or makeh b’patish (finishing touches). As such, one must be sure to cut toilet paper before Shabbat or use tissues that are dispensed one-by-one. Indeed, a roll of toilet paper is muktza on Shabbat and may not be used or moved unless one is faced with no alternative, as will be explained below.
In the event that one did not prepare toilet paper or tissues before Shabbat, one may hint, or if need be, directly ask a non-Jew to cut some toilet paper. One who realizes while using the washroom that there is no pre-cut toilet paper available should ideally use the toilet paper directly from the roll without tearing it. One can then drop the used portion into the toilet and then flush it down the toilet. In fact, one can unroll a bit more toilet paper than what was actually used in order to ensure that all the soiled toilet paper will be flushed away.
The above solution will not always be practical, of course. So too, it is likely to offend others who must use the same washroom. Therefore, one who feels that the above method is impractical or should not be used is permitted to tear the toilet paper. The tear should preferably be made between the perforated lines rather than along them. One should also not tear the toilet paper to any specific length – one should simply estimate how much one will need. So too, one should tear the toilet paper with a shinui, in an irregular manner, such as with one's fists or with fingers that are not usually used for this purpose.
One of the reasons that it is permitted to cut toilet paper in this way on Shabbat is due to the principle of kavod habriot, which teaches that certain rabbinical prohibitions may be waived for the sake of human dignity. One might also want to consider washing oneself with soap and water, and drying oneself with a cloth or towel rather than tearing toilet paper at all, should it be an option. Indeed, it is actually considered superior and more meticulous to always use baby wipes or other water based means to clean oneself. It is permissible to open a package of tissues (that dispense one-by-one) on Shabbat in a manner that destroys the packaging in the process. One should be careful though not to cut through any words in the process of opening such a package.
One who is in a washroom as Shabbat concludes and must rip toilet paper, or perform any other melacha for that matter, should envision the "baruch hamavdil…" formula in one's mind. This is considered to be an adequate form of havdalla, considering the circumstances, to permit ripping the toilet paper. Other authorities disagree with this approach, ruling that even thinking the “baruch hamavdil…” formula in a washroom is forbidden. According to this view, one must conduct oneself as if it were still Shabbat, using one of the solutions mentioned above.
One who is in a hotel or hospital, where the bathrooms are equipped with electronic sensors that automatically flush the toilets after they are used, is permitted to use such a toilet on Shabbat when no other option exists. This too is for considerations of kavod habriot. It is interesting to note that in ancient times people were discouraged from cleaning themselves with their right hand due to its distinct status in the performance of mitzvot. Since nowadays we use toilet paper, and the like, there is no concern or preference as to which hand one should use when cleaning oneself.
 Shemirat Shabbat K'hilchata 23:16.
 See for example, OC 340:13; Mishna Berura 340:41; Rivevot Ephraim 7:234; Shevet Halevi 1:115; Tzitz Eliezer 11:30; Minchat Shlomo 2:12:5; Az Nidberu 1:79; Or L'tzion 2:40:6; Pe'at Sadecha 2:87; Mishne Halachot 6:84, 11:271.
 Shalmei Yehuda p. 98, 171. See also Rema, OC 312:1.
 Shemirat Shabbat K'hilchata 30:8 note 22; Shraga Hameir 8:22:1.
 Ribiat p. 843.
 Shulchan Aruch Harav 340:17; Shemirat Shabbat K'hilchata 23:16 and Tikunim Umiluim, 23 note 55; Rivevot Ephraim 6:193; Shraga Hameir 8:22:1; Yabia Omer 8:39; Avnei Yashfei 1:77. See also Rema, OC 312:1; Mishna Berura 312:8; Chelkat Yaakov, OC 3:123; Shevet Hakehati 2:117; Shemesh Umagen 1:4; Shevet Halevi 1:115; Tzitz Eliezer 11:30.
 Berachot 19b; Shemirat Shabbat K’hilchata 23:16; Tzitz Eliezer 11:30. See also Rema, OC 312:1.
 Avnei Yashfei 1:77.
 OC 76:7; Mishna Berura 76:18; Shulchan Aruch Harav, OC 3:8; Kaf Hachaim, OC 3:75, 76:26.
 Rivevot Ephraim 8:287; Shaarei Yosher 3:56. It may even be permitted to say the “baruch hamavdil…” formula out loud. See the sources cited here for more.
 Shabbat 40b; Rambam, Hilchot Kriat Shema 3:4; OC 85:2; Avnei Yashfei 6:10:1.
 Magen Avraham 3:8; Taz 3:9.
 Tzitz Eliezer 7:2.