\documentclass{article}
\begin{document}
Including a LilyPond file without any options:
+
\lilypondfile{include2.ly}
+
+From a subdirectory:
+
+\lilypondfile{include/example.ly}
+
+Within a lilypond block:
+
+\begin{lilypond}
+ \include "include/myvar.ily"
+ \relative c'' { \myVar }
+\end{lilypond}
\end{document}