I keep the whole sefira. 1st day shloshes yemay hagbola is Sunday. Can I have a haircut before Shabbos?
In halachic terms, it would appear that it is permitted to take a haircut on erev Shabbos. This is based on the same principle as when Lag Ba’Omer falls on Sunday, in which case one may take a haircut on Friday, in honor of Shabbos. This ruling is given by the Peri Megadim (Eishel Avraham 493:5; see also Zeh Hashulchan 1:493).
However, there are poskim who disagree with the Peri Megadim, and rule that one would not be permitted to take a haircut even on Friday. See Rabbi Elimelech Bluth, LeTorah VeHoraah vol. 10, p.14, quoting from Rav Moshe Feinstein, who makes several distinctions between the Friday before Lag Ba’Omer and the Friday before the commencement of the yemei hagbalah. See also Chochmas Shlomo, commenting on the Peri Megadim, and Chasam Sofer.
Despite this, where there is some need, one may be lenient in following the ruling of the Peri Megadim.
However, if you keep the entire sefira out of kabbalistic reasons, the no-haircut period will include Friday.