cat

cat prints the contents of the files specified as arguments to the terminal. This is handy as the first command of a pipeline, for example, cat foo.txt | blah.

sort

sort prints the contents of the file specified on the command line in alphabetical order. Of course, sort also accepts piped input. Type man sort to familiarize yourself with its various options that control sorting behavior.

uniq

uniq takes an already sorted file or stream of data (via a pipeline) and removes duplicate lines.