Splice["file"] splices Mathematica output into an external file. It takes text enclosed between <* and *> in the file, evaluates the text as Mathematica input, and replaces the text with the resulting Mathematica output.
Splice["infile", "outfile"] processes text from the file infile, and writes output into outfile.
Splice["file"] takes files with names of the form name.mx and writes output in files with names name.x.
Text in the input file not enclosed between <* and *> is copied without change to the output file.
The default format for Mathematica output is determined by the extension of the input file name:
The following options for Splice can be used:
You can use pipes instead of files for input and output to Splice.
See The Mathematica Book: Section 1.11.9.
See also: RunThrough.