Roland Ver. 4.5 Informações Técnicas descarregar pdf (Página 63)

Chapter 5: Writing Recipes in Rules 53

variable := value

export variable

Likewise,

export variable += value

is just like:

variable += value

export variable

See Section 6.6 [Appending More Text to Variables], page 66.

You may notice that the export and unexport directives work in make in the same way

they work in the shell, sh.

If you want all variables to be exported by default, you can use export by itself:

export

This tells make that variables which are not explicitly mentioned in an export or unexport

directive should be exported. Any variable given in an unexport directive will still not be

exported. If you use export by itself to export variables by default, variables whose names

contain characters other than alphanumerics and underscores will not be exported unless

speciﬁcally mentioned in an export directive.

The behavior elicited by an export directive by itself was the default in older versions of

GNU make. If your makeﬁles depend on this behavior and you want to be compatible with

old versions of make, you can write a rule for the special target .EXPORT_ALL_VARIABLES

instead of using the export directive. This will be ignored by old makes, while the export

directive will cause a syntax error.

Likewise, you can use unexport by itself to tell make not to export variables by default.

Since this is the default behavior, you would only need to do this if export had been used

by itself earlier (in an included makeﬁle, perhaps). You cannot use export and unexport

by themselves to have variables exported for some recipes and not for others. The last

export or unexport directive that appears by itself determines the behavior for the entire

run of make.

As a special feature, the variable MAKELEVEL is changed when it is passed down from

level to level. This variable’s value is a string which is the depth of the level as a decimal

number. The value is ‘0’ for the top-level make; ‘1’ for a sub-make, ‘2’ for a sub-sub-make,

and so on. The incrementation happens when make sets up the environment for a recipe.

The main use of MAKELEVEL is to test it in a conditional directive (see Chapter 7 [Con-

ditional Parts of Makeﬁles], page 77); this way you can write a makeﬁle that behaves one

way if run recursively and another way if run directly by you.

You can use the variable MAKEFILES to cause all sub-make commands to use additional

makeﬁles. The value of MAKEFILES is a whitespace-separated list of ﬁle names. This variable,

if deﬁned in the outer-level makeﬁle, is passed down through the environment; then it serves

as a list of extra makeﬁles for the sub-make to read before the usual or speciﬁed ones. See

Section 3.4 [The Variable MAKEFILES], page 14.

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Roland Ver. 4.5 Informações Técnicas Página 63