On Thu, 2 Jun 2005, Stepan Kasal wrote:
> it uses test "x$VAR" = x
>
> Thus the manual should use the term "is nonempty", not "is set".
>
> (One of the reasons for this behaviour is that unset is not portable.)
It's documented that the builtin `unset' is non-portable, but what about
the use of unset variables vs. empty variables? Is this distinction
always meaningful? (Some of the caveats about MS DOS suggest not?) Also,
I know that ${var:-default} is not portable. Is ${var-default}? For that
matter, I know you can set bash to error out on $var for an unset var,
which would require ${var-}. I'm ignorant: is this behavior turned off
by AC_INIT (or whatever)?
-Dan
This patch is not entirely correct.
We should used "is nonempty" instead of "is set".
And it's possible that I'm also missing something else.
2004-10-27 Stepan Kasal <kasal@xxxxxx>
* doc/autoconf.texi (Alternative Programs): Rename the node to ...
(Programs): ... this. Add a general information, ...
(Generic Programs): ... removing it from the description of
individual macros.
(Particular Programs, AC_PROG_GREP): Improve a formulation.
--- doc/autoconf.texi.a2 2004-10-27 11:12:47.000000000 +0200
+++ doc/autoconf.texi 2004-10-27 11:31:27.000000000 +0200
@@ -325,7 +325,7 @@
Existing Tests
* Common Behavior:: Macros' standard schemes
-* Alternative Programs:: Selecting between alternative programs
+* Programs:: Selecting between alternative programs
* Files:: Checking for the existence of files
* Libraries:: Library archives that might be missing
* Library Functions:: C library functions that might be missing
@@ -342,7 +342,7 @@
* Standard Symbols:: Symbols defined by the macros
* Default Includes:: Includes used by the generic macros
-Alternative Programs
+Programs
* Particular Programs:: Special handling to find certain programs
* Generic Programs:: How to find other programs
@@ -3078,7 +3078,7 @@
@menu
* Common Behavior:: Macros' standard schemes
-* Alternative Programs:: Selecting between alternative programs
+* Programs:: Selecting between alternative programs
* Files:: Checking for the existence of files
* Libraries:: Library archives that might be missing
* Library Functions:: C library functions that might be missing
@@ -3212,16 +3212,38 @@
@code{HAVE_STRINGS_H} won't.
@end defmac
-@node Alternative Programs
-@section Alternative Programs
+@node Programs
+@section Programs
@cindex Programs, checking
These macros check for the presence or behavior of particular programs.
-They are used to choose between several alternative programs and to
-decide what to do once one has been chosen. If there is no macro
-specifically defined to check for a program you need, and you don't need
-to check for any special properties of it, then you can use one of the
-general program-check macros.
+They are also used to choose between several alternative programs and to
+decide what to do once one has been chosen.
+
+If there is no macro specifically defined to check for a program you
+need, and you don't need to check for any special properties of it, then
+you can use one of the general program-check macros.
+
+These macros work with an environment variable, eg.@ @code{GREP}; for
+the generic macros, you specify the variable name as the first
+parameter.
+
+If the variable is already set, the macro does nothing.
+
+If it is not set, it looks for the program. If the program is found,
+it's name is assigned to the variable. (Or name with parameters, or
+full pathname, it depends on the individual macros.) If the program is
+not found and the optional parameter @var{value-if-not-found} was
+specified, that value is assigned to the variable.
+
+All these macros call AC_SUBST on the variable.
+
+As the result depends on the initial value of the variable, it should
+be declared as precious. This is done automatically by the specific
+tests. For the generic macros, you are strongly encouradged to declare
+the variable as precious, @xref{Setting Output Variables},
+@code{AC_ARG_VAR}, for more details. (Another possibility would be
+to unset the variable before calling the macro.)
@menu
* Particular Programs:: Special handling to find certain programs
@@ -3252,8 +3274,8 @@
single @option{-e} option. This macro looks for @sc{gnu} Grep or
else the best available @code{grep} or @code{ggrep} in the user's
@code{$PATH} which accepts the longest input lines possible, and which
-accepts and respects multiple @option{-e} options. Set the
-output variable @code{GREP} to whatever is chosen.
+accepts and respects multiple @option{-e} options. It sets the output
+variable @code{GREP} to whatever is chosen.
@end defmac
@defmac AC_PROG_EGREP
@@ -3433,9 +3455,7 @@
@var{value-if-not-found}, if given. Always pass over @var{reject} (an
absolute file name) even if it is the first found in the search path; in
that case, set @var{variable} using the absolute file name of the
-@var{prog-to-check-for} found that is not @var{reject}. If
-@var{variable} was already set, do nothing. Calls @code{AC_SUBST} for
-@var{variable}.
+@var{prog-to-check-for} found that is not @var{reject}.
@end defmac
@defmac AC_CHECK_PROGS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
@@ -3444,9 +3464,8 @@
@var{progs-to-check-for} existing in the @env{PATH}. If one is found, set
@var{variable} to the name of that program. Otherwise, continue
checking the next program in the list. If none of the programs in the
-list are found, set @var{variable} to @var{value-if-not-found}; if
-@var{value-if-not-found} is not specified, the value of @var{variable}
-is not changed. Calls @code{AC_SUBST} for @var{variable}.
+list are found, set @var{variable} to @var{value-if-not-found} (if it is
+specified).
@end defmac
@defmac AC_CHECK_TARGET_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
@@ -3496,9 +3515,7 @@
prefix, and if the build and target types are equal, then the first one
without a prefix is used. If a tool is found, set @var{variable} to
the name of that program. If none of the tools in the list are found,
-set @var{variable} to @var{value-if-not-found}; if @var{value-if-not-found}
-is not specified, the value of @var{variable} is not changed. Calls
-@code{AC_SUBST} for @var{variable}.
+set @var{variable} to @var{value-if-not-found}, if it is given.
@end defmac
@defmac AC_CHECK_TOOLS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path})
@@ -3509,9 +3526,8 @@
(@pxref{Canonicalizing}). If none of the tools can be found with a
prefix, then the first one without a prefix is used. If a tool is found,
set @var{variable} to the name of that program. If none of the tools in
-the list are found, set @var{variable} to @var{value-if-not-found}; if
-@var{value-if-not-found} is not specified, the value of @var{variable}
-is not changed. Calls @code{AC_SUBST} for @var{variable}.
+the list are found, set @var{variable} to @var{value-if-not-found}, if
+specified.
In the future, when cross-compiling this macro will @emph{not}
accept program names that are not prefixed with the host type.
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