Re: brace expansion fails in 4.3, succeed in 4.2

[Dan Douglas]

On Saturday, May 10, 2014 02:35:44 PM NBaH wrote:
> bash-4.2 $ printf "%s " "$(date -d -"{0..9}"days +%Y%m%d)" 20140510
> 20140509 20140508 20140507 20140506 20140505 20140504 20140503
> 20140502 20140501
>
> bash-4.3 $ printf "%s " "$(date -d -"{0..9}"days +%Y%m%d)" date: date
> non valide « -{0..9}days »

This was a bug. Chet fixed it for 4.3. The inner brace expansion should
not be evaluated because (non-backtick) command substitutions always
produce a completely new context for evaluating commands.

Since bash re-arranges Csh brace expansion to be first, it has to
heuristically protect the applicable expansions that happen later from
its effects. That's a hard problem.

You can achieve the same effect in other ways by looping or with eval if
appropriate. printf %()T is another possibility. I usually abuse the way
Bash parses array subscripts. If ksh93 is available then a simpler
solution is possible.

 $ bash -c 'printf -v a "%(%s)T" -1; printf "%(%Y%m%d)T " "$a" 
"${a[a+=60*60*24,0]"{0..8}"}"; echo'
20140510 20140511 20140512 20140513 20140514 20140515 20140516 20140517 
20140518 20140519
 $ ksh -c 'printf "%(%Y%m%d)T " "" -{1..9}\ days; echo'
20140510 20140511 20140512 20140513 20140514 20140515 20140516 20140517 
20140518 20140519

--
Dan Douglas