Actually the non-Chasidic (Ashkenaz) haredim follow the Shulchan Aruch with the Rema's additions, as do other Ashkenazim.

When more clarification is needed, they (and all frum Jews) will consult the Nosei Keilim (commentaries) printed on the page and the back of the volume. 

A deeper understanding of how the Halacha came to be, would require opening the Tur (of which the Shulchan Aruch is essentially a summary) and the Rambam, after learning the relevant Gemara with Rif, Ran and Rosh.

If that fails - or they want a shortcut - they may consult popular classic works that use the Shulchan Aruch as a basis. Popular ones are:


The Mishnah Berura on Orach Chaim
The Aruch Hashulchan on all 4 parts of Shulchan Aruch (with some omissions, some apparently got lost as it was originally published as small booklets.)
The Shulchan Aruch HaRav (from the Ba'al HaTanya)


Alternately - or if the above doesn't solve their specific problem - they will consult compendiums like the Chayei Adam or Kitzur Shulchan Aruch, or more recent works as described in an earlier answer.

Nowadays you can find Sefarim that deal exclusively with almost any topic, and they usually highlight Ashkenazi/Hassidich/Sefardi differences, when they exist.

Litvaks/Yeshivish and Shulchan Aruch
I need to be able to alphabetically sort the output of find before piping it to a command. Entering | sort | between didn't work, so what could I do?

find folder1 folder2 -name "*.txt" -print0 | xargs -0 myCommand

