LilyPond Benutzerhandbuch: A.10.5 Conditionals

### A.10.5 Conditionals

`\if` condition? (procedure) argument (markup)

  Test condition, and only insert argument if it is true. The condition is provided as a procedure taking an output definition and a property alist chain. The procedure is applied, and its result determines whether to print the markup. This command is most useful inside `oddHeaderMarkup` or similar. Here is an example printing page numbers in bold:

  >     \paper {
  >       oddHeaderMarkup =
  >         \markup \fill-line {
  >           ""
  >           \if #print-page-number
  >                \bold \fromproperty #'page:page-number-string
  >         }
  >       evenHeaderMarkup =
  >         \markup \fill-line {
  >           \if #print-page-number
  >                \bold \fromproperty #'page:page-number-string
  >           ""
  >         }
  >     }

`\unless` condition? (procedure) argument (markup)

  Similar to `\if`, printing the argument if the condition is false.

  The following example shows how to print the copyright notice on all pages but the last instead of just the first page.

  >     \paper {
  >       oddFooterMarkup = \markup {
  >         \unless #on-last-page-of-part \fill-line {
  >           \fromproperty #'header:copyright
  >         }
  >       }
  >     }

  >     \header {
  >       copyright = "© LilyPond Authors. License: GFDL."
  >       tagline = "© LilyPond Authors.  Documentation placed
  >     under the GNU Free Documentation License
  >     version 1.3."
  >     }

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