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Further improve docs about nested double-quotes and backquotes.

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* doc/autoconf.texi (Shellology): Remove anchor for pdksh.
Move quoting bug example to ...
(Shell Substitutions): ... here.  Document which behavior is
specified by Posix.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
This commit is contained in:
Ralf Wildenhues 2010-06-23 19:55:02 +02:00
parent c14e7a1c8a
commit d11a65ced6
2 changed files with 23 additions and 18 deletions
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6
ChangeLog
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@ -1,5 +1,11 @@
2010-06-23 Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
Further improve docs about nested double-quotes and backquotes.
* doc/autoconf.texi (Shellology): Remove anchor for pdksh.
Move quoting bug example to ...
(Shell Substitutions): ... here. Document which behavior is
specified by Posix.
Coverage for Fortran compiler macros.
* tests/fortran.at (AC_OPENMP and Fortran 77)
(AC_OPENMP and Fortran): Simplify, using AT_CHECK_CONFIGURE.

35
doc/autoconf.texi
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@ -14639,7 +14639,6 @@ the standard shell conform to Posix.
@item Pdksh
@prindex @samp{pdksh}
@anchor{pdksh}
A public-domain clone of the Korn shell called @command{pdksh} is widely
available: it has most of the @samp{ksh88} features along with a few of
its own. It usually sets @code{KSH_VERSION}, except if invoked as
@ -14647,20 +14646,7 @@ its own. It usually sets @code{KSH_VERSION}, except if invoked as
Posix compatibility by running @samp{set -o posix}. Unfortunately, with
@command{pdksh} 5.2.14 (the latest stable version as of January 2007)
Posix mode is buggy and causes @command{pdksh} to depart from Posix in
at least one respect:
@example
$ @kbd{echo "`echo \"hello\"`"}
hello
$ @kbd{set -o posix}
$ @kbd{echo "`echo \"hello\"`"}
"hello"
@end example
The last line of output contains spurious quotes. This is yet another
reason why portable shell code should not contain
@code{"`@dots{}\"@dots{}\"@dots{}`"} constructs (@pxref{Shell
Substitutions}).
at least one respect, see @ref{Shell Substitutions}.
@item Zsh
@cindex Zsh
@ -15163,9 +15149,22 @@ ksh: bar | sed 's, ,,': cannot execute
@end example
@noindent
Worse yet, not all shells understand @code{"`@dots{}\"@dots{}\"@dots{}`"}
the same way (@pxref{pdksh}). There is just no portable way to use double-quoted
strings inside double-quoted back-quoted expressions (pfew!).
Posix does not specify behavior for this sequence. On the other hand,
behavior for @code{"`@dots{}\"@dots{}\"@dots{}`"} is specified by Posix,
but in practice, not all shells understand it the same way: pdksh 5.2.14
prints spurious quotes when in Posix mode:
@example
$ @kbd{echo "`echo \"hello\"`"}
hello
$ @kbd{set -o posix}
$ @kbd{echo "`echo \"hello\"`"}
"hello"
@end example
@noindent
There is just no portable way to use double-quoted strings inside
double-quoted back-quoted expressions (pfew!).
@table @code
@item $@@