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docs: mention bash bug with word splitting

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* doc/autoconf.texi (Shell Substitutions): Document bash bug, and
zsh default behavior difference.
Reported by Ralf Wildenhues.
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Eric Blake 2010-08-03 15:56:07 -06:00
parent 608c89c8c6
commit 5adc15b7b6
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@ -1,5 +1,10 @@
2010-08-03 Eric Blake <eblake@redhat.com>
docs: mention bash bug with word splitting
* doc/autoconf.texi (Shell Substitutions): Document bash bug, and
zsh default behavior difference.
Reported by Ralf Wildenhues.
docs: mention ksh bug with function syntax
* doc/autoconf.texi (Shell Functions): Document ksh93 limitation.

26
doc/autoconf.texi
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@ -15283,6 +15283,32 @@ $ @kbd{echo "`echo \"hello\"`"}
There is just no portable way to use double-quoted strings inside
double-quoted back-quoted expressions (pfew!).
Bash 4.1 has a bug where quoted empty strings adjacent to unquoted
parameter expansions are elided during word splitting. Meanwhile, zsh
does not perform word splitting except when in Bourne compatibility
mode. In the example below, the correct behavior is to have five
arguments to the function, and exactly two spaces on either side of the
middle @samp{-}, since word splitting collapses multiple spaces in
@samp{$f} but leaves empty arguments intact.
@example
$ @kbd{bash -c 'n() @{ echo "$#$@@"; @}; f=" - "; n - ""$f"" -'}
3- - -
$ @kbd{ksh -c 'n() @{ echo "$#$@@"; @}; f=" - "; n - ""$f"" -'}
5- - -
$ @kbd{zsh -c 'n() @{ echo "$#$@@"; @}; f=" - "; n - ""$f"" -'}
3- - -
$ @kbd{zsh -c 'emulate sh;}
> @kbd{n() @{ echo "$#$@@"; @}; f=" - "; n - ""$f"" -'}
5- - -
@end example
@noindent
You can work around this by doing manual word splitting, such as using
@samp{"$str" $list} rather than @samp{"$str"$list}.
There are also portability pitfalls with particular expansions:
@table @code
@item $@@
@cindex @samp{"$@@"}