RunThrough["command", expr] executes an external command, giving the printed form of expr as input, and taking the output, reading it as Mathematica input, and returning the result.
RunThrough is not available on all computer systems.
RunThrough writes the InputForm of expr on the standard input for command, then reads its standard output, and feeds it into Mathematica.
RunThrough starts command, then gives input to command, then terminates the input.
See The Mathematica Book: Section 2.11.2.
See also: Install, Put, Get, Splice.