@c @fuindex strerror_r
@prindex @code{strerror_r}
POSIX specifies that @code{strerror_r} returns an @code{int}, but many
-systems (e.g., GNU C Library version 2.36) provide a
+systems (e.g., the GNU C Library) provide a
different version returning a @code{char *}. @code{AC_FUNC_STRERROR_R}
can detect which is in use (@pxref{Particular Functions}).
variable.
This macro is obsolescent, as current systems have a @code{getpgrp}
-whose signature conforms to POSIX. New programs need not use this macro.
+whose signature conforms to POSIX@. New programs need not use this macro.
@end defmac
@defmac AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK
and @code{SELECT_TYPE_ARG5} defaults to @samp{struct timeval *}.
This macro is obsolescent, as current systems have a @code{select} whose
-signature conforms to POSIX. New programs need not use this macro.
+signature conforms to POSIX@. New programs need not use this macro.
@end defmac
@defmac AC_FUNC_SETPGRP
@code{char *} message, define @code{STRERROR_R_CHAR_P}; otherwise it
returns an @code{int} error number. The Thread-Safe Functions option of
POSIX requires @code{strerror_r} to return @code{int}, but
-many systems (including, for example, version 2.2.4 of the GNU C
+many systems (including, for example, the GNU C
Library) return a @code{char *} value that is not necessarily equal to
the buffer argument.
This macro caches its result in the @code{ac_cv_header_sys_wait_h}
variable.
-This macro is obsolescent, as current systems are compatible with POSIX.
+This macro is obsolescent, as current systems are compatible with POSIX@.
New programs need not use this macro.
@end defmac
not a POSIX system. However, some non-POSIX systems do
have @file{unistd.h}.
-The way to check whether the system supports POSIX is:
+The way to check whether the system says it supports POSIX is:
@example
@group
@defmacx m4_maketemp (@var{template})
@msindex{maketemp}
@msindex{mkstemp}
-POSIX requires @code{maketemp} to replace the trailing @samp{X}
+Older versions of POSIX specified a macro @code{maketemp},
+which replaced the trailing @samp{X}
characters in @var{template} with the process id, without regards to the
-existence of a file by that name, but this a security hole. When this
-was pointed out to the POSIX folks, they agreed to invent a new macro
-@code{mkstemp} that always creates a uniquely named file, but not all
-versions of GNU M4 support the new macro. In M4sugar,
+existence of a file by that name.
+This was a security hole, so current POSIX instead specifies a macro
+@code{mkstemp} that always creates a uniquely named file. In M4sugar,
@code{m4_maketemp} and @code{m4_mkstemp} are synonyms for each other,
and both have the secure semantics regardless of which macro the
underlying M4 provides.
disk volume or disk image formatted as case sensitive; this can be done
using the @command{diskutil} command or the Disk Utility application.
-@item QNX 4.25
-@cindex QNX 4.25
+@item QNX
+@cindex QNX
@c FIXME: Please, if you feel like writing something more precise,
@c it'd be great. In particular, I can't understand the difference with
@c QNX Neutrino.
QNX is a realtime operating system running on Intel architecture
meant to be scalable from the small embedded systems to the hundred
-processor super-computer. It claims to be POSIX certified. More
+processor super-computer. More
information is available on the
@uref{https://@/blackberry.qnx.com/@/en, QNX home page}.
@prindex @samp{ksh88}
@prindex @samp{ksh93}
The Korn shell is compatible with the Bourne family and it mostly
-conforms to POSIX. It has two major variants commonly
+conforms to POSIX@. It has two major variants commonly
called @samp{ksh88} and @samp{ksh93}, named after the years of initial
release. It is usually called @command{ksh}, but is called @command{sh}
on some hosts if you set your path appropriately.
its own. It usually sets @code{KSH_VERSION}, except if invoked as
@command{/bin/sh} on OpenBSD, and similarly to Bash you can require
POSIX compatibility by running @samp{set -o posix}. Unfortunately, with
-@command{pdksh} 5.2.14 (the latest stable version as of January 2007)
+@command{pdksh} 5.2.14 (the latest stable version as of 2025)
POSIX mode is buggy and causes @command{pdksh} to depart from POSIX in
at least one respect, see @ref{Shell Substitutions}.
good ones.
If you intend to redirect both standard error and standard output,
-redirect standard output first. This works better with HP-UX,
+redirect standard output first. This works better with AIX,
since its shell mishandles tracing if standard error is redirected
first:
@noindent
As a workaround, @command{echo} or @command{eval} can be used.
-Don't rely on file descriptors 0, 1, and 2 remaining closed in a
+When running a subsidiary program be careful if descriptor 0 is not open
+for reading or decriptors 1 and 2 are not open for writing,
+as the subsidiary program might not behave as expected.
+In particular, don't rely on file descriptors 0, 1, and 2 remaining closed in a
subsidiary program. If any of these descriptors is closed, the
operating system may open an unspecified file for the descriptor in the
-new process image. POSIX 2008 says this may be done only if the
-subsidiary program is set-user-ID or set-group-ID, but HP-UX 11.23 does
-it even for ordinary programs, and the next version of POSIX will allow
-HP-UX behavior.
+newly created process.
If you want a file descriptor above 2 to be inherited into a child
process, then you must use redirections specific to that command or a
When this variable is set it specifies a list of directories to search
when invoking @code{cd} with a relative file name that did not start
with @samp{./} or @samp{../}. POSIX
-1003.1-2001 says that if a nonempty directory name from @env{CDPATH}
+says that if a nonempty directory name from @env{CDPATH}
is used successfully, @code{cd} prints the resulting absolute
file name. Unfortunately this output can break idioms like
@samp{abs=`cd src && pwd`} because @code{abs} receives the name twice.
@item POSIXLY_CORRECT
@evindex POSIXLY_CORRECT
In the GNU environment, exporting @env{POSIXLY_CORRECT} with any value
-(even empty) causes programs to try harder to conform to POSIX.
+(even empty) causes programs to try harder to conform to POSIX@.
Autoconf does not directly manipulate this variable, but @command{bash}
ties the shell variable @env{POSIXLY_CORRECT} to whether the script is
running in POSIX mode. Therefore, take care when exporting or unsetting
@item PWD
@evindex PWD
-POSIX 1003.1-2001 requires that @command{cd} and
-@command{pwd} must update the @env{PWD} environment variable to point
-to the logical name of the current directory, but traditional shells
+POSIX requires that @command{cd}
+must update the @env{PWD} environment variable to point
+to the name of the current directory, but traditional shells
do not support this. This can cause confusion if one shell instance
maintains @env{PWD} but a subsidiary and different shell does not know
about @env{PWD} and executes @command{cd}; in this case @env{PWD}
@item @command{cd}
@c ---------------
@prindex @command{cd}
-POSIX 1003.1-2001 requires that @command{cd} must support
+POSIX requires that @command{cd} must support
the @option{-L} (``logical'') and @option{-P} (``physical'') options,
with @option{-L} being the default. However, traditional shells do
not support these options, and their @command{cd} command has the
directory names are in contrast to ``physical'' directory names, whose
components are all directories.
-POSIX 1003.1-2001 requires that @command{pwd} must support
+POSIX requires that @command{pwd} must support
the @option{-L} (``logical'') and @option{-P} (``physical'') options,
with @option{-L} being the default. However, traditional shells do
not support these options, and their @command{pwd} command has the
To test for symbolic links on systems that have them, use
@samp{test -h} rather than @samp{test -L}; either form conforms to
-POSIX 1003.1-2001, but @option{-h} has been around longer.
+POSIX, but @option{-h} has been around longer.
The commands @samp{test A -ot B} and @samp{test A -nt B} are not reliable
on macOS @command{sh} through at least macOS Sequoia 15.1.1 (2024),
Traditional Awk implementations derived from Unix version 7, such as
Solaris @command{/bin/awk}, have many limitations and do not
-conform to POSIX. Nowadays @code{AC_PROG_AWK} (@pxref{Particular
+conform to POSIX@. Nowadays @code{AC_PROG_AWK} (@pxref{Particular
Programs}) finds you an Awk that doesn't have these problems, but if
for some reason you prefer not to use @code{AC_PROG_AWK} you may need to
address them. For more detailed descriptions, see @ref{Language
@end itemize
The C compiler's traditional name is @command{cc}, but other names like
-@command{gcc} are common. POSIX 1003.1-2001 through 1003.1-2017 specify the
-name @command{c99}, but older POSIX editions specified
-@command{c89}, future POSIX standards will likely specify
+@command{gcc} are common. POSIX 1003.1-2024 specifies the
+name @command{c17}, but older POSIX editions specified
+@command{c99} or @command{c89}, future POSIX standards will likely specify
other commands, and anyway these standard names are rarely used in
practice. Typically the C compiler is invoked from makefiles that use
@samp{$(CC)}, so the value of the @samp{CC} make variable selects the
should be portable nowadays.
The replacement of @samp{@{@}} is guaranteed only if the argument is
-exactly @emph{@{@}}, not if it's only a part of an argument. For
-instance, on HP-UX 11:
+exactly @samp{@{@}}, not if @samp{@{@}} only a part of a larger argument.
+For instance, on AIX 7.3:
@example
$ @kbd{touch foo}
-$ @kbd{find . -name foo -exec echo "@{@}-@{@}" \;}
+$ @kbd{find . -name foo -exec echo '@{@}-@{@}' \;}
@{@}-@{@}
@end example
while GNU @command{find} reports @samp{./foo-./foo}.
POSIX allows either behavior.
-
@anchor{grep}
@item @command{grep}
@c -----------------
projects / thirdparty / autoconf.git / commitdiff
