SQLet allows you to directly execute SQL on multiple text files, right from the Linux commandline. In one single command, you can read in text files (with or without header lines) and perform arbitrary select statements, including joins over several files. SQLet can thus replace awk or grep in some instances.
tblutils is a collection of several utilities for working with tabular text files: data written in plain text, with one row per line and columns separated by a common character (usually TAB or semicolon). It complements the usual Unix tools like cut and paste by providing enhanced versions that support column labels through-out, so that you can extract columns by name (tblcut), filter data using a mathematical expression (tblfilter), re-order columns without caring about the column index (tblcsort), join multiple files on a common index without having to pre-sort them (tblmerge), and much more.