Shkoyach! (Jewish Link article preview)

In shul, after a person has completed his aliyah and is en-route to his seat, I am in the habit of congratulating him by telling him “Shkoyach”. However, on Shabbat and Yom Tov, I avoid doing so, taking my lead from Yehuda HaLevi’s zemer Yona Matza, which instructs: “Yom Shabbason ain liShkoyach.”

Really, though, “Shkoyach” is an informal way of expressing, as a hurried contraction of יְיַשֶּׁר כּוֹחֲךָ or יִישַׁר כֹּוֹחֲךָ. This was already a common expression in endorsing someone’s actions in Amoraic times, and Reish Lakish plays on this when, in Shabbat 87a and several parallel sugyot, he interprets Hashem’s referring to the tablets Moshe broke, אֲשֶׁר שִׁבַּרְתָּ, as יִישַׁר כֹּחֲךָ שֶׁשִּׁבַּרְתָּ, “congratulations that you broke it!” 

The expression was also in use in Tannaitic times. In Yevamot 122b,