On 05/12/2014 10:33 AM, Jim Meyering wrote:
> Does anyone see a way to make it more efficient with a POSIX shell?

Yes. Eric's earlier message convinced me that grep shouldn't rely on 
Autoconf guaranteeing a shell that supports substrings in parameter 
expansion, so I came up with the attached patch (which keeps the shell 
efficient with a POSIX shell) and pushed it before I got around to 
reading your message.  I tested on Solaris 10 with the shell 
artificially set to /bin/sh, so I'm marking this as done.

 From an Autoconf point of view it might be nice to have a good way to 
say "I need a POSIX shell" or at least "I need a shell that does 
substrings", but that's merely a wishlist item.