Based on a report by Michael Felt, via Paul Eggert on the coreutils list. * doc/autoconf.texi (Limitations of Builtins) <for>: Document problem with 'for var in ;'.
Signed-off-by: Eric Blake <[email protected]> --- doc/autoconf.texi | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) diff --git a/doc/autoconf.texi b/doc/autoconf.texi index 8c4302d..bbc9fa3 100644 --- a/doc/autoconf.texi +++ b/doc/autoconf.texi @@ -17757,6 +17757,40 @@ Limitations of Builtins word splitting on @samp{$@{1+"$@@"@}}; see @ref{Shell Substitutions}, item @samp{$@@}, for more. +Posix requires support for a @command{for} loop with no list after +@code{in}. However, Solaris @command{/bin/sh} treats that as a syntax +error. It is possible to work around this by providing any shell word +that expands to nothing, or by ignoring an obvious sentinel. + +@example +$ @kbd{/bin/sh -c 'for a in $empty; do echo hi; done'} +$ @kbd{/bin/sh -c 'for a in ; do echo hi; done'} +/bin/sh: syntax error at line 1: `;' unexpected +@end example + +The problem is most common in makefile fragments where a make variable +is used as the source of a list, but sometimes results in no text. In +that context, another common workaround is to use a shell variable +rather than a make variable as the source of the list. + +@example +$ @kbd{cat Makefile} +list = +bad: + @@for arg in $(list); do echo $$arg; done +good: + @@list='$(list)'; for arg in $$list; do echo $$arg; done +$ @kbd{make bad list='a b'} +a +b +$ @kbd{make bad 2&>1 | head -n1} +sh: syntax error at line 1: `;' unexpected +$ @kbd{make good} +$ @kbd{make good list='a b'} +a +b +@end example + In Solaris @command{/bin/sh}, when the list of arguments of a @command{for} loop starts with @emph{unquoted} tokens looking like variable assignments, the loop is not executed on those tokens: -- 2.4.2
