mirror of
git://git.sv.gnu.org/autoconf
synced 2025-02-17 14:01:27 +08:00
* doc/autoconf.texi: Lots of additions and changes.
(File Descriptors): New. (Limitations of Make): New.
This commit is contained in:
Akim Demaille
parent
4c6ce32f58
commit
10498c169e
@ -1,3 +1,9 @@
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2001-01-16 Akim Demaille <akim@epita.fr>
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* doc/autoconf.texi: Lots of additions and changes.
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(File Descriptors): New.
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(Limitations of Make): New.
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2001-01-16 Akim Demaille <akim@epita.fr>
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* m4sh.m4 (AS_EXIT): Don't rely on exit == exit $?.
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@ -704,7 +704,7 @@ gives unlimited permission to copy, distribute and modify it.])dnl
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m4_define([AS_MESSAGE_FD], 6)
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m4_define([AS_MESSAGE_LOG_FD], 5)
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# That's how trey used to be named.
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# That's how they used to be named.
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AU_ALIAS([AC_FD_CC], [AS_MESSAGE_LOG_FD])
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AU_ALIAS([AC_FD_MSG], [AS_MESSAGE_FD])
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@ -713,8 +713,6 @@ m4_define([_AC_INIT_DEFAULTS_FDS],
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# 0 standard input
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# 1 file creation
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# 2 errors and warnings
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# 3 some systems may open it to /dev/tty
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# 4 used on the Kubota Titan
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@%:@ AS_MESSAGE_FD checking for... messages and results
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@%:@ AS_MESSAGE_LOG_FD compiler messages saved in config.log
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if test "$silent" = yes; then
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@ -3719,9 +3717,8 @@ test "x$prefix" = xNONE && prefix=$ac_default_prefix
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# Let make expand exec_prefix.
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test "x$exec_prefix" = xNONE && exec_prefix='${prefix}'
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# Any assignment to VPATH causes Sun make to only execute
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# the first set of double-colon rules, so remove it if not needed.
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# If there is a colon in the path, we need to keep it.
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# VPATH is dangerous, but if there is a colon in the path, we need to
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# keep it.
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if test "x$srcdir" = x.; then
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ac_vpsub=['/^[ ]*VPATH[ ]*=[^:]*$/d']
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fi
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@ -207,8 +207,8 @@ Existing Tests
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* Structures:: Structures or members that might be missing
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* Types:: Types that might be missing
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* Compilers and Preprocessors:: Checking for compiling programs
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* C Compiler Characteristics::
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* Fortran 77 Compiler Characteristics::
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* C Compiler:: Checking its characteristics
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* Fortran 77 Compiler:: Checking its characteristics
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* System Services:: Operating system services
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* UNIX Variants:: Special kludges for specific UNIX variants
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@ -267,11 +267,13 @@ Checking Run Time Behavior
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Portable Shell Programming
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* Shellology:: A zoology of shells
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* Shell Substitutions:: Variable expansions...
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* File Descriptors:: FDs and redirections
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* Shell Substitutions:: Variable and command expansions
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* Assignments:: Varying side effects of assignments
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* Special Shell Variables:: Variables you should not change
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* Limitations of Builtins:: Portable use of not so portable /bin/sh
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* Limitations of Usual Tools:: Portable use of portable tools
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* Limitations of Make:: Portable Makefiles
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Results of Tests
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@ -2571,8 +2573,8 @@ Symbols}, for how to get those symbol definitions into your program.
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* Structures:: Structures or members that might be missing
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* Types:: Types that might be missing
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* Compilers and Preprocessors:: Checking for compiling programs
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* C Compiler Characteristics::
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* Fortran 77 Compiler Characteristics::
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* C Compiler:: Checking its characteristics
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* Fortran 77 Compiler:: Checking its characteristics
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* System Services:: Operating system services
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* UNIX Variants:: Special kludges for specific UNIX variants
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@end menu
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@ -4062,7 +4064,7 @@ implemented. In case of doubt, read the documentation of the former
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@code{AC_CHECK_TYPE}, see @ref{Obsolete Macros}.
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@node Compilers and Preprocessors, C Compiler Characteristics, Types, Existing Tests
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@node Compilers and Preprocessors, C Compiler, Types, Existing Tests
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@section Compilers and Preprocessors
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@ovindex EXEEXT
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@ -4253,7 +4255,7 @@ this is becoming a less prevalent problem.
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@end defmac
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@node C Compiler Characteristics, Fortran 77 Compiler Characteristics, Compilers and Preprocessors, Existing Tests
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@node C Compiler, Fortran 77 Compiler, Compilers and Preprocessors, Existing Tests
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@section C Compiler Characteristics
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The following macros check for C compiler or machine architecture
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@ -4410,7 +4412,7 @@ defines @code{SIZEOF_INT_P} to be 8 on DEC Alpha AXP systems.
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@node Fortran 77 Compiler Characteristics, System Services, C Compiler Characteristics, Existing Tests
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@node Fortran 77 Compiler, System Services, C Compiler, Existing Tests
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@section Fortran 77 Compiler Characteristics
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The following macros check for Fortran 77 compiler characteristics. To
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@ -4522,7 +4524,7 @@ preprocessor as above; for example, to call Fortran routines from some
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language other than C/C++.
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@end defmac
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@node System Services, UNIX Variants, Fortran 77 Compiler Characteristics, Existing Tests
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@node System Services, UNIX Variants, Fortran 77 Compiler, Existing Tests
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@section System Services
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The following macros check for operating system services or capabilities.
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@ -5053,14 +5055,16 @@ Some of these external utilities have a portable subset of features, see
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@menu
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* Shellology:: A zoology of shells
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* Shell Substitutions:: Variable expansions...
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* File Descriptors:: FDs and redirections
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* Shell Substitutions:: Variable and command expansions
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* Assignments:: Varying side effects of assignments
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* Special Shell Variables:: Variables you should not change
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* Limitations of Builtins:: Portable use of not so portable /bin/sh
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* Limitations of Usual Tools:: Portable use of portable tools
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* Limitations of Make:: Portable Makefiles
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@end menu
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@node Shellology, Shell Substitutions, Portable Shell, Portable Shell
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@node Shellology, File Descriptors, Portable Shell, Portable Shell
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@subsection Shellology
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There are several families of shells, most prominently the Bourne
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@ -5071,15 +5075,15 @@ family.
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Below we describe some of the members of the Bourne shell family.
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@table @asis
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@item @command{ash}
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@cindex @command{ash}
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@item Ash
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@cindex Ash
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@command{ash} is often used on @sc{gnu}/Linux and @sc{bsd} systems as a
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light-weight Bourne-compatible shell. @command{ash} version 0.2 has
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some bugs that are fixed in the 0.3.x series, but portable shell scripts
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should workaround them, since version 0.2 is still shipped with many
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@sc{gnu}/Linux distributions.
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light-weight Bourne-compatible shell. Ash 0.2 has some bugs that are
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fixed in the 0.3.x series, but portable shell scripts should workaround
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them, since version 0.2 is still shipped with many @sc{gnu}/Linux
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distributions.
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To be compatible with @command{ash} 0.2
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To be compatible with Ash 0.2:
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@itemize @bullet
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@item
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@ -5100,18 +5104,13 @@ echo $@{FOO=`bar`@}
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@end example
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@item
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beware that @command{exit} inside command substitution causes the
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current shell to exit as well. Use parentheses to prevent @command{ash}
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from exiting:
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@example
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(`exit 1`) || echo "All right"
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`exit 1` || echo "ash won't print it"
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@end example
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beware that single builtin substitutions are not performed by a sub
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shell, hence their effect applies to the current shell! @xref{Shell
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Substitutions}, item ``Command Substitution''.
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@end itemize
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@item @command{bash}
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@cindex @command{bash}
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@item Bash
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@cindex Bash
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To detect whether you are running @command{bash}, test if
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@code{BASH_VERSION} is set. To disable its extensions and require
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@sc{posix} compatibility, run @samp{set -o posix}. @xref{Bash POSIX
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@ -5125,8 +5124,8 @@ The @sc{posix}-compliant Bourne shell on a Solaris system is
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There is no extra charge for this package, but it is also not part of a
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minimal OS install and therefore some folks may not have it.
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@item @command{zsh}
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@cindex @command{zsh}
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@item Zsh
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@cindex Zsh
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To detect whether you are running @command{zsh}, test if
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@code{ZSH_VERSION} is set. By default @command{zsh} is @emph{not}
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compatible with the Bourne shell: you have to run @samp{emulate sh} and
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@ -5162,13 +5161,45 @@ So while most modern systems do have a shell _somewhere_ that meets the
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@sc{posix} standard, the challenge is to find it.
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@end quotation
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@node File Descriptors, Shell Substitutions, Shellology, Portable Shell
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@subsection File Descriptors
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@node Shell Substitutions, Assignments, Shellology, Portable Shell
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Some file descriptors shall not be used, since some systems, admittedly
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arcane, use them for special purpose:
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@table @asis
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@item 3
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some systems may open it to @samp{/dev/tty}.
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@item 4
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used on the Kubota Titan.
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@end table
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Don't redirect several times the same file descriptor, as you are doomed
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to failure under Ultrix.
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@example
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ULTRIX V4.4 (Rev. 69) System #31: Thu Aug 10 19:42:23 GMT 1995
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UWS V4.4 (Rev. 11)
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$ eval 'echo matter >fullness' >void
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illegal io
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$ eval '(echo matter >fullness)' >void
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illegal io
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$ (eval '(echo matter >fullness)') >void
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Ambiguous output redirect.
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@end example
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@noindent
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In each case the expected result is of course @file{fullness} containing
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@samp{matter} and @file{void} being empty.
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@node Shell Substitutions, Assignments, File Descriptors, Portable Shell
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@subsection Shell Substitutions
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Contrary to a persistent urban legend, the Bourne shell does not
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systematically split variables and backquoted expressions, in
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particular, the following code:
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systematically split variables and backquoted expressions, in particular
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on the right-hand side of assignments, and the argument of @code{case}.
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For instance the following code:
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@example
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case "$given_srcdir" in
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@ -5178,8 +5209,7 @@ esac
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@end example
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@noindent
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is more readable with the right-hand side of the assignments, and the
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argument of @code{case} left without quotes:
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is more readable written as:
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@example
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case $given_srcdir in
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@ -5201,7 +5231,7 @@ inside double-quoted backquoted expressions (Pfew!).
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@cindex @samp{"$@@"}
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One of the most famous shell portability issues is related to
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@samp{"$@@"}: when there are no positional argument, it is supposed to
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be equivalent to nothing. But some shell, for instance under Digital
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be equivalent to nothing. But some shells, for instance under Digital
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Unix 4.0 and 5.0, will then replace it with an empty argument. To be
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portable, use @samp{$@{1+"$@@"@}}.
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@ -5310,6 +5340,27 @@ test "$@{var+set@}" = set || var=@var{@{value@}}
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@end example
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@item `@var{commands}`
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@cindex `@var{commands}`
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@cindex Command Substitution
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While in general it makes no sense, do not substitute a single builtin
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with side effects as Ash 0.2, trying to optimize, does not fork a sub
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shell to perform the command.
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For instance if you wanted to check that @command{cd} is silent, do not
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use @samp{test -z "`cd /tmp`"} because...
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@example
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$ pwd
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/tmp
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$ test -n "`cd /`" && pwd
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/
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@end example
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@noindent
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The result of @samp{foo=`exit 1`} is left as an exercise to the reader.
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@item $(@var{commands})
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@cindex $(@var{commands})
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This construct is meant to replace @samp{`@var{commands}`}; they can be
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@ -5589,7 +5640,7 @@ as the string composed of a backslash and an n.
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@c -----------------
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@cindex @command{exit}
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The default value of @command{exit} is supposed to be @code{$?},
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unfortunately some shell, such as the @sc{djgpp} port of Bash 2.04, just
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unfortunately some shells, such as the @sc{djgpp} port of Bash 2.04, just
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perform @samp{exit 0}.
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@example
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@ -5686,6 +5737,7 @@ done
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@end example
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@item @command{if}
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@c ---------------
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@cindex @command{if}
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Using @samp{!} is not portable. Instead of
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@ -5704,6 +5756,28 @@ if cmp -s file file.new; then :; else
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fi
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@end example
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There are shells which do not reset the exit status out of an
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@command{if}:
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@example
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$ if (exit 42); then true; fi; echo $?
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42
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@end example
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@noindent
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while a proper shell should have printed @samp{0}. This is especially
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bad in Makefiles since it produces false failures. This is why properly
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written Makefiles, such as Automake's, have such hairy constructs:
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@example
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if test -f "$file"; then
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install "$file" "$dest"
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else
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:
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fi
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@end example
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@item @command{set}
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@c ----------------
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@cindex @command{set}
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@ -5746,6 +5820,7 @@ You may use @samp{!} with @command{test}, but not with @command{if}:
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@samp{test ! -r foo || exit 1}.
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@item @command{test} (files)
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@c -------------------------
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To enable @code{configure} scripts to support cross-compilation, they
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shouldn't do anything that tests features of the build system instead of
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the host system. But occasionally you may find it necessary to check
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@ -5755,6 +5830,7 @@ have it. Do not use @samp{test -e} either, because Solaris 2.5 does not
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have it.
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@item @command{test} (strings)
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@c ---------------------------
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Avoid @samp{test "@var{string}"}, in particular if @var{string} might
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start with a dash, since @code{test} might interpret its argument as an
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option (e.g., @samp{@var{string} = "-n"}).
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@ -5914,7 +5990,7 @@ $unset CDPATH || CDPATH=:
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the case of environment variables.
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@end table
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@node Limitations of Usual Tools, , Limitations of Builtins, Portable Shell
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@node Limitations of Usual Tools, Limitations of Make, Limitations of Builtins, Portable Shell
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@subsection Limitations of Usual Tools
|
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The small set of tools you can expect to find on any machine can still
|
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@ -6295,6 +6371,20 @@ s/.*/deleted/g
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@end example
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@end table
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@node Limitations of Make, , Limitations of Usual Tools, Portable Shell
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@subsection Limitations of Make
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Make itself suffers a great number of limitations, only a few of which
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being listed here. First of all, remember that since commands are
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executed by the shell, all its weaknesses are inherited...
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@table @asis
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@item @code{VPATH}
|
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@cindex @code{VPATH}
|
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Don't use it! For instance any assignment to @code{VPATH} causes Sun
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@command{make} to only execute the first set of double-colon rules.
|
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@end table
|
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|
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|
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@node Multiple Cases, Language Choice, Portable Shell, Writing Tests
|
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@section Multiple Cases
|
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|
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@ -704,7 +704,7 @@ gives unlimited permission to copy, distribute and modify it.])dnl
|
||||
|
||||
m4_define([AS_MESSAGE_FD], 6)
|
||||
m4_define([AS_MESSAGE_LOG_FD], 5)
|
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# That's how trey used to be named.
|
||||
# That's how they used to be named.
|
||||
AU_ALIAS([AC_FD_CC], [AS_MESSAGE_LOG_FD])
|
||||
AU_ALIAS([AC_FD_MSG], [AS_MESSAGE_FD])
|
||||
|
||||
@ -713,8 +713,6 @@ m4_define([_AC_INIT_DEFAULTS_FDS],
|
||||
# 0 standard input
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||||
# 1 file creation
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||||
# 2 errors and warnings
|
||||
# 3 some systems may open it to /dev/tty
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||||
# 4 used on the Kubota Titan
|
||||
@%:@ AS_MESSAGE_FD checking for... messages and results
|
||||
@%:@ AS_MESSAGE_LOG_FD compiler messages saved in config.log
|
||||
if test "$silent" = yes; then
|
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@ -3719,9 +3717,8 @@ test "x$prefix" = xNONE && prefix=$ac_default_prefix
|
||||
# Let make expand exec_prefix.
|
||||
test "x$exec_prefix" = xNONE && exec_prefix='${prefix}'
|
||||
|
||||
# Any assignment to VPATH causes Sun make to only execute
|
||||
# the first set of double-colon rules, so remove it if not needed.
|
||||
# If there is a colon in the path, we need to keep it.
|
||||
# VPATH is dangerous, but if there is a colon in the path, we need to
|
||||
# keep it.
|
||||
if test "x$srcdir" = x.; then
|
||||
ac_vpsub=['/^[ ]*VPATH[ ]*=[^:]*$/d']
|
||||
fi
|
||||
|
||||
Loading…
Reference in New Issue
Block a user