mercury/extras/split_file

Copyright (C) 2020 The Mercury team

As its name says, split_file is a utility program that helps its users to
split one file into two or more pieces. The intended use case is splitting up
a Mercury module into several smaller modules, though of course there are
many other possible uses.

Editing the file to be split up and cutting and pasting selecting sections
of it to other editor windows open on the destination files is tedious.
Duplicating a file and then deleting alternating sections from the original
and its copy is error prone; it is far too easy to have a part end up
unintentionally in both copies, or none. In both cases, errors are hard
to recover from.

With split_file, the user can mark up the original source file
(or better still, a *copy* of that source file) with control lines
such as "SPLIT 1", "SPLIT 2" and "SPLIT 1 3". When the marked-up file
is given to split_file as the input, with the names of three output files,
each block of data lines (the lines between control lines) will end up
in the output file(s) whose number(s) are on the control line preceding
the block. In the event of an error, one can just discard both output files,
modify the markup, and repeat the invocation of split_file.