4.1.1 Introduction to the LilyPond file structure

A basic example of a LilyPond input file is

\version "2.25.21"

\header { }

\score {
   … compound music expression …   % all the music goes here!
  \layout { }
  \midi { }
}

There are many variations of this basic pattern, but this example serves as a useful starting place.

Up to this point none of the examples you have seen have used a \score command. This is because LilyPond automatically adds the extra commands that are needed when you give it simple input. LilyPond treats input like this:

\relative {
  c''4 a b c
}

as shorthand for this:

\book {
  \score {
    \new Staff {
      \new Voice {
        \relative {
          c''4 a b c
        }
      }
    }
    \layout { }
  }
}

In other words, if the input contains a single music expression, LilyPond will interpret the file as though the music expression was wrapped up inside the commands shown above.

A word of warning! Many of the examples in the LilyPond documentation will omit the \new Staff and \new Voice commands, leaving them to be created implicitly. For simple examples this works well, but for more complex examples, especially when additional commands are used, the implicit creation of contexts can give surprising results, maybe creating extra unwanted staves. For a detailed explanation how to create contexts explicitly, see Contexts and engravers.

For now, though, let us return to the first example and examine the \score command, leaving the others to default.

A \score block must always contain exactly one music expression. Remember that a music expression could be anything from a single note to a huge compound expression like

{
  \new StaffGroup <<
     … insert the whole score of a Wagner opera in here … 
  >>
}

Since everything is inside { … }, it counts as one music expression.

As we saw previously, the \score block can contain other things, such as

\score {
  { c'4 a b c' }
  \header { }
  \layout { }
  \midi { }
}

Note that these three commands – \header, \layout, and \midi – are special: unlike many other commands that begin with a backward slash (\) they are not music expressions and are not part of any music expression. So they may be placed inside a \score block or outside it. In fact, these commands are commonly placed outside the \score block – for example, \header is often placed above the \score command, as the example at the beginning of this section shows.

Two more commands you have not previously seen are \layout and \midi. If these appear as shown they will cause LilyPond to produce a printed output and a MIDI output, respectively. They are described fully in the Notation Reference – Score layout, and Creating MIDI output.

You may code multiple \score blocks. Each will be treated as a separate score, but they will be all combined into a single output file. A \book command is not necessary – one will be implicitly created. However, if you would like separate output files from one .ly file then the \book command should be used to separate the different sections: each \book block will produce a separate output file.

To summarize:

• Every \book block creates a separate output file (e.g., a PDF file). If you haven’t explicitly added one, LilyPond wraps your entire input code in a \book block implicitly.
• Every \score block is a separate chunk of music within a \book block.
• Every \layout block affects the \score or \book block in which it appears – i.e., a \layout block inside a \score block affects only that \score block, but a \layout block outside of a \score block (and thus in a \book block, either explicitly or implicitly) will affect every \score in that \book.

See Multiple scores in a book for details.

Another great shorthand is the ability to define variables, as shown previously (see Organizing pieces with variables). All the templates use this:

melody = \relative {
  c'4 a b c
}

\score {
  \melody
}

When LilyPond looks at this file, it takes the value of melody (everything after the equals sign) and inserts it whenever it sees \melody. There’s nothing special about the name – it could be melody, global, keyTime, pianorighthand, or something else. Remember that you can use almost any name you like as long as it contains just alphabetic characters and is distinct from LilyPond command names. For more details, see Saving typing with variables and functions. The exact limitations on variable names are detailed in File structure.

See also

For a complete definition of the input format, see File structure.