File: make.info,  Node: Multi-Line,  Next: Undefine Directive,  Prev: Override Directive,  Up: Using Variables

6.8 Defining Multi-Line Variables
=================================

Another way to set the value of a variable is to use the 'define'
directive.  This directive has an unusual syntax which allows newline
characters to be included in the value, which is convenient for defining
both canned sequences of commands (*note Defining Canned Recipes: Canned
Recipes.), and also sections of makefile syntax to use with 'eval'
(*note Eval Function::).

   The 'define' directive is followed on the same line by the name of
the variable being defined and an (optional) assignment operator, and
nothing more.  The value to give the variable appears on the following
lines.  The end of the value is marked by a line containing just the
word 'endef'.

   Aside from this difference in syntax, 'define' works just like any
other variable definition.  The variable name may contain function and
variable references, which are expanded when the directive is read to
find the actual variable name to use.

   The final newline before the 'endef' is not included in the value; if
you want your value to contain a trailing newline you must include a
blank line.  For example in order to define a variable that contains a
newline character you must use _two_ empty lines, not one:

     define newline


     endef

   You may omit the variable assignment operator if you prefer.  If
omitted, 'make' assumes it to be '=' and creates a recursively-expanded
variable (*note The Two Flavors of Variables: Flavors.).  When using a
'+=' operator, the value is appended to the previous value as with any
other append operation: with a single space separating the old and new
values.

   You may nest 'define' directives: 'make' will keep track of nested
directives and report an error if they are not all properly closed with
'endef'.  Note that lines beginning with the recipe prefix character are
considered part of a recipe, so any 'define' or 'endef' strings
appearing on such a line will not be considered 'make' directives.

     define two-lines
     echo foo
     echo $(bar)
     endef

   When used in a recipe, the previous example is functionally
equivalent to this:

     two-lines = echo foo; echo $(bar)

since two commands separated by semicolon behave much like two separate
shell commands.  However, note that using two separate lines means
'make' will invoke the shell twice, running an independent sub-shell for
each line.  *Note Recipe Execution: Execution.

   If you want variable definitions made with 'define' to take
precedence over command-line variable definitions, you can use the
'override' directive together with 'define':

     override define two-lines =
     foo
     $(bar)
     endef

*Note The 'override' Directive: Override Directive.