So today is Moshe Rabbeinu's Yahrzeit, and there are many people in the streets commemorating this by wearing green and drinking. There is also a large prevalence of bagpipes. I was wondering what the source for this minhag is.
The bagpipes are a type of horn. We blow horns on Moshe's yahrtzeit to commemorate the horns on Moshe's skin as stated:
וַיְהִ֗י בְּרֶ֤דֶת מֹשֶׁה֙ מֵהַ֣ר סִינַ֔י וּשְׁנֵ֨י לֻחֹ֤ת הָֽעֵדֻת֙ בְּיַד־מֹשֶׁ֔ה בְּרִדְתּ֖וֹ מִן־הָהָ֑ר וּמֹשֶׁ֣ה לֹֽא־יָדַ֗ע כִּ֥י קָרַ֛ן ע֥וֹר פָּנָ֖יו בְּדַבְּר֥וֹ אִתּֽוֹ׃
And it came to pass, when Moses came down from mount Sinai with the two tables of the testimony in Moses’ hand, when he came down from the mount, that Moses knew not that the skin of his face sent forth horns while He talked with him.
Wearing green is because regarding Moshe's sister, Miriam, it says:
וַיֹּ֨אמֶר יְהוָ֜ה אֶל־מֹשֶׁ֗ה וְאָבִ֙יהָ֙ יָרֹ֤ק יָרַק֙ בְּפָנֶ֔יהָ הֲלֹ֥א תִכָּלֵ֖ם שִׁבְעַ֣ת יָמִ֑ים תִּסָּגֵ֞ר שִׁבְעַ֤ת יָמִים֙ מִח֣וּץ לַֽמַּחֲנֶ֔ה וְאַחַ֖ר תֵּאָסֵֽף׃
And the LORD said unto Moses: ‘If her father had made her face greenish, should she not hide in shame seven days? let her be shut up without the camp seven days, and after that she shall be brought in again.’
Miriam was envious of Moshe's beautiful wife, and usuall envious people are green. But since Miriam became leprous, she turned white instead of green, and Moshe prayed for Miriam's healing. Moshe was a humble man, so in the merit of his prayers, even though G-d had said, "If only her father would have made her green", that would have happened, when she was envious. However, since she was envious of such a humble person such as Moshe, she turned white instead of green, all in Moshe's merit.
The drinking minhag is easier to explain. Moshe's yahrtzeit is exactly 1 week before Purim. Getting drunk on this date is practice for Purim. (Note, that drinking on Moshe's yahrtziet is not a universal minhag. Some people are not allowed to get drunk for health reasons, and others can drink a ton of beer and never get drunk.) However, we want to guarantee that there is at least one Shabbat between Moshe's yahrtzeit and Purim so that people can rest from their stupor and let it wear off. If it were less than a week, people might still be drunk when reading the Megilla if there was no intervening Shabbat. More than 1 week, and they might feel out of practice. Also, beer, the cheapest alcoholic beverage, loses almost all of its strength after a week. Thus, the minhag to drink on Moshe's yahrtzeit, a week before Purim.