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* doc/make.texi (Variables/Recursion): [SV 56446] Clarify export docs

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Paul Smith 2022-08-14 14:05:07 -04:00
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doc/make.texi
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@ -3171,10 +3171,10 @@ for a particular run of @code{make}, use the @samp{-s} or
@findex .EXPORT_ALL_VARIABLES
@item .EXPORT_ALL_VARIABLES
Simply by being mentioned as a target, this tells @code{make} to
export all variables to child processes by default.
@xref{Variables/Recursion, ,Communicating Variables to a
Sub-@code{make}}.
Simply by being mentioned as a target, this tells @code{make} to export all
variables to child processes by default. This is an alternative to using
@code{export} with no arguments. @xref{Variables/Recursion, ,Communicating
Variables to a Sub-@code{make}}.
@findex .NOTPARALLEL
@item .NOTPARALLEL
@ -4795,10 +4795,8 @@ initialize its table of variable values. @xref{Environment,
,Variables from the Environment}.
Except by explicit request, @code{make} exports a variable only if it
is either defined in the environment initially or set on the command
line, and if its name consists only of letters, numbers, and underscores.
Some shells cannot cope with environment variable names consisting of
characters other than letters, numbers, and underscores.
is either defined in the environment initially, or if set on the command
line and its name consists only of letters, numbers, and underscores.
@cindex SHELL, exported value
The value of the @code{make} variable @code{SHELL} is not exported.
@ -4904,31 +4902,39 @@ export
@end example
@noindent
This tells @code{make} that variables which are not explicitly mentioned
in an @code{export} or @code{unexport} directive should be exported.
Any variable given in an @code{unexport} directive will still @emph{not}
be exported. If you use @code{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 @code{export} directive.@refill
This tells @code{make} that variables which are not explicitly mentioned in an
@code{export} or @code{unexport} directive should be exported. Any variable
given in an @code{unexport} directive will still @emph{not} be exported.
@findex .EXPORT_ALL_VARIABLES
The behavior elicited by an @code{export} directive by itself was the
default in older versions of GNU @code{make}. If your makefiles depend
on this behavior and you want to be compatible with old versions of
@code{make}, you can write a rule for the special target
@code{.EXPORT_ALL_VARIABLES} instead of using the @code{export} directive.
This will be ignored by old @code{make}s, while the @code{export}
directive will cause a syntax error.@refill
@cindex compatibility in exporting
The behavior elicited by an @code{export} directive by itself was the default
in older versions of GNU @code{make}. If your makefiles depend on this
behavior and you want to be compatible with old versions of @code{make}, you
can add the special target @code{.EXPORT_ALL_VARIABLES} to your makefile
instead of using the @code{export} directive. This will be ignored by old
@code{make}s, while the @code{export} directive will cause a syntax
error.
Likewise, you can use @code{unexport} by itself to tell @code{make}
@emph{not} to export variables by default. Since this is the default
behavior, you would only need to do this if @code{export} had been used
by itself earlier (in an included makefile, perhaps). You
@strong{cannot} use @code{export} and @code{unexport} by themselves to
have variables exported for some recipes and not for others. The last
@code{export} or @code{unexport} directive that appears by itself
When using @code{export} by itself or @code{.EXPORT_ALL_VARIABLES} to export
variables by default, only variables whose names consist solely of
alphanumerics and underscores will be exported. To export other variables you
must specifically mention them in an @code{export} directive.
Adding a variable's value to the environment requires it to be expanded. If
expanding a variable has side-effects (such as the @code{info} or @code{eval}
or similar functions) then these side-effects will be seen every time a
command is invoked. You can avoid this by ensuring that such variables have
names which are not exportable by default. However, a better solution is to
@emph{not} use this ``export by default'' facility at all, and instead
explicitly @code{export} the relevant variables by name.
You can use @code{unexport} by itself to tell @code{make} @emph{not} to export
variables by default. Since this is the default behavior, you would only need
to do this if @code{export} had been used by itself earlier (in an included
makefile, perhaps). You @strong{cannot} use @code{export} and @code{unexport}
by themselves to have variables exported for some recipes and not for others.
The last @code{export} or @code{unexport} directive that appears by itself
determines the behavior for the entire run of @code{make}.@refill
@vindex MAKELEVEL