6.8 Defining Variables Verbatim

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 (see Defining Canned Command Sequences), and also sections of makefile syntax to use with eval (see Eval Function).

The define directive is followed on the same line by the name of the variable 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 `=': it creates a recursively-expanded variable (see The Two Flavors of Variables). 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.

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 tab characters are considered part of a command script, so any define or endef strings appearing on such a line will not be considered make operators.

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

The value in an ordinary assignment cannot contain a newline; but the newlines that separate the lines of the value in a define become part of the variable's value (except for the final newline which precedes the endef and is not considered part of the value).

When used in a command script, 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 subshell for each line. See Command 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

See The override Directive.