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[SV 65359] doc/make.texi: Describe invalid export variable names

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Paul Smith 2024-03-24 14:05:45 -04:00
parent 3176b60566
commit 21a538ce8f
1 changed files with 20 additions and 9 deletions
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doc/make.texi
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@ -4974,6 +4974,15 @@ In both of these forms, the arguments to @code{export} and
@code{unexport} are expanded, and so could be variables or functions
which expand to a (list of) variable names to be (un)exported.
GNU Make will add any variable you export to the environment of all child
processes. However, be aware that some child processes themselves will not
accept all types of variables. For example, many modern shells will clean the
incoming environment by removing or hiding any environment variable whose name
is invalid for the shell (e.g., alphanumeric plus underscore). There is
nothing GNU Make can do about the behavior of these child processes: if you
want your makefile to be maximally portable you should choose simple variable
names for all exported variables.
As a convenience, you can define a variable and export it at the same
time by doing:
@ -5036,15 +5045,10 @@ 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@r{, compatibility}
@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.
@findex .EXPORT_ALL_VARIABLES
Another way to export variables by default is to add the special target
@code{.EXPORT_ALL_VARIABLES} to your makefile. This will be ignored by other
variants of @code{make}.
When using @code{export} by itself or @code{.EXPORT_ALL_VARIABLES} to export
variables by default, only variables whose names consist solely of
@ -5059,6 +5063,13 @@ 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.
Be aware that exporting all variables can have serious performance impacts,
especially for recursive variables used in conjunction with the @code{shell}
function. We recommend you avoid this and instead export only the specific
variables needed to run your commands. If you do need to export all
variables, use simple variable assignment wherever possible, especially when
invoking the @code{shell} function.
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