My friends and I were learning about the way that the Jews camped in the wilderness, and someone heard about a book called Degel Machane Efrayim. Does anyone know who wrote it and where I can find it?
As @DoubleAA rightly pointed out, there's more than one work called Degel Machane Ephraim. The one I'm most familiar with - and what I think is the most well-known one - is a Chassidic work by Rabbi Moshe Chaim Ephraim of Sudkilov, grandson of the Baal Shem Tov (and, incidentally, is an ancestor of mine...). His book in Hebrew can be accessed here. It's a commentary on the Pentateuch.
Other such works are by Rabbi Ephraim Laniado, chief rabbi of Aleppo (his book in Hebrew can be found here) and by Rabbi Ephraim Shteinberg, who was a rabbi at RIETS (his book, a halachic work, in Hebrew can be accessed here).
Note that these three are the only ones listed, both in Hebrewbooks and in Otzar Hachochmah.