init.ly, what does it do?

[Br. Samuel Springuel]

Can someone explain to me what the functionality of the init.ly file is? 
 In particular I'm trying to figure out if I could write one which is 
specific to a particular project so that I can use the same ly source 
for two different projects and yet produce different output versions by 
simply invoking lilypond with the appropriate --init option on the source.

For example, project 1 is simply producing the scores by themselves and 
thus needs no extras, while project 2 would involve inserting a score 
(or pieces there of) into another document and thus involves the use of 
the lilypond-book-preamble.ly (or rather a customized version thereof).

In this example then, `lilypond sample.ly` would produce the project 1 
scores while `lilypond --init="my_init.ly" sample.ly` would produce the 
project 2 system-by-system files.
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Br. Samuel, OSB
St. Anselm’s Abbey
Washington, DC
(R. Padraic Springuel)

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