@ovindex EXEEXT
All the tests for compilers (@code{AC_PROG_CC}, @code{AC_PROG_CXX},
@code{AC_PROG_F77}) define the output variable @code{EXEEXT} based on
-the output of the compiler, after @samp{.$ac_ext} (i.e. source files of
-the current language), @samp{.o}, @samp{.obj} and @samp{.xcoff} files
-have been excluded. Typically set to empty string if Unix and
+the output of the compiler. Typically set to empty string if Unix and
@samp{.exe} if Win32 or OS/2.
@ovindex CYGWIN
correct. This is a problem that Autoconf does not currently handle
automatically. If users encounter this problem, they might be able to
solve it by setting @code{LDFLAGS} in the environment to pass whatever
-options the linker needs (for example, @option{-Wl,-dn} on MIPS RISC/OS).
+options the linker needs (for example, @option{-Wl,-dn} on @sc{mips
+risc/os}).
@code{AC_TRY_LINK} is used to compile test programs to test for
functions and global variables. It is also used by @code{AC_CHECK_LIB}
@noindent
otherwise some shells, such as on Digital Unix V 5.0, will die because
-of a @emph{bad substitution}.
+of a ``bad substitution''.
When setting several variables in a row, be aware that the order of the
evaluation is undefined. For instance @samp{foo=1 foo=2; echo $foo}
-gives @samp{1} with sh on Solaris, but @samp{2} with bash. You must use
+gives @samp{1} with sh on Solaris, but @samp{2} with Bash. You must use
@samp{;} to enforce the order: @samp{foo=1; foo=2; echo $foo}.
+@cindex @samp{"$@@"}
+One of the most famous shell portability issues is related to
+@samp{"$@@"}: when there are no positional argument, it is supposed to
+be equivalent to nothing. But some shell, for instance under Digital
+Unix 4.0 and 5.0, will then replace it with an empty argument. To be
+portable, use @samp{$@{1+"$@@"@}}.
+
Contrary to a persistent urban legend, the Bourne shell does not
systematically split variables and backquoted expressions, in
particular, the following code:
@cindex @command{break}
The use of @samp{break 2} etc. is safe.
+@item @command{!}
+@cindex @command{!}
+You can't use @command{!}, you'll have to rewrite your code.
+
@item @command{case}
@cindex @command{case}
You don't need to quote the argument, no splitting is performed.
Do not use backslashes in the arguments, as there is no consensus on
their handling:
-On @samp{foo='\n'; echo "$foo" | wc -l}, the @command{sh} of Digital
-Unix 4.0, RISC/os 4.52, answer 2, but the Solaris' @command{sh}, Bash
-and Zsh (in @command{sh} emulation mode) report 1.
+On @samp{echo '\n' | wc -l}, the @command{sh} of Digital Unix 4.0,
+@sc{mips risc/os} 4.52, answer 2, but the Solaris' @command{sh}, Bash
+and Zsh (in @command{sh} emulation mode) report 1. Please note that the
+problem is truly @command{echo}: all the shells understand @samp{'\n'}
+as the string composed of a backslash and an n.
@item @command{exit}
@cindex @command{exit}
fi
@end example
+@item @command{set}
+@cindex @command{set}
+This builtin faces the usual problem with arguments starting with a
+dash. Modern shells, such as Bash or Zsh understand @samp{--} to
+specify the end of the options (any argument behind @samp{--} is an
+parameters, even @samp{-x} for instance), but most shell simply stop the
+option processing as soon as a non option argument is found. Therefore
+use @samp{dummy} or simply @samp{x} to neutralize the option processing,
+and use @command{shift} to pop it out:
+
+@example
+set x $my_list; shift
+@end example
+
@item @command{shift}
@cindex @command{shift}
Not only is @command{shift}ing a bad idea when there is nothing left to
-shift, but in addition it is not portable: the shell of @sc{RISC/os}
-4.52 refuses it.
+shift, but in addition it is not portable: the shell of @sc{mips
+risc/os} 4.52 refuses it.
@item @command{test}
@cindex @command{test}
Do compilation tests using the compiler, preprocessor and file
extensions for the @var{language}.
-Support languages are:
+Supported languages are:
@table @samp
@item C
[ac_cv_emxos2=no])])
@end example
+When using @code{AC_TRY_RUN} or any macro which cannot work when
+cross-compiling, provide a pessimistic value (typically @samp{no}).
Feel free to use various tricks to avoid that auxiliary tools, such as
syntax-highlighting editors, behave improperly. For instance, instead
@noindent
otherwise, the closing bracket would be hidden inside a @samp{#}-comment
-breaking the bracket matching highlighting from Emacsen.
+breaking the bracket matching highlighting from Emacsen. Note the
+preferred style to escape from M4: @samp{$[1]}, @samp{$[@@]} etc. Do
+not escape when it is unneeded. Common examples of useless quotation
+are @samp{[$]$1} (write @samp{$$1}), @samp{[$]var} (use @samp{$var}),
+etc. If you add portability issues to the picture, you'll prefer
+@samp{$@{1+"$[@@]"@}} to @samp{"[$]@@"}, and you'll prefer do something
+better than hacking Autoconf @code{:-)}.
When using @command{sed}, don't use @option{-e} but for indenting
purpose. With the @code{s} command, the preferred separator is @samp{/}
@ovindex EMXOS2
@ovindex MINGW32
Defined the output variable @code{EXEEXT} based on the output of the
-compiler, after @samp{.$ac_ext} (i.e. source files of the current
-language), @samp{.o}, @samp{.obj} and @samp{.xcoff} files have been
-excluded. Typically set to empty string if Unix and @samp{.exe} if
+compiler. Typically set to empty string if Unix and @samp{.exe} if
Win32 or OS/2.
This macro sets the shell variable @code{CYGWIN} to @samp{yes} if run in
projects / thirdparty / autoconf.git / commitdiff
