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  • grep uses regular expressions to search for strings in files. Some good online resources to understand it are at robelle.com and at thegeekstuff.com (http://www.thegeekstuff.com/2011/01/advanced-regular-expressions-in-grep-command-with-10-examples-–-part-ii/)
  • awk is an actual programming language, like perl or python. But it's built-in to linux, is very general-purpose, and is ideal for parsing & filtering large text files.
  • uniq simply recognizes when two or more adjacent lines are the same. Some useful switches: -c counts how many identical lines there were and prepends the count to the line itself, -w N only uses the first N characters of each line to decide if they're the same.
  • sort orders a bunch of lines. It's very fast and memory efficient - sorting a few million lines on a current linux system should only take a few minutes.

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