Re: Confusing/unclear documentation of Sed back references

[Eric Blake]

On 11/26/2014 12:54 PM, Bob Proulx wrote:

>> This is no longer entirely true.  POSIX has proposed standardizing the
>> -E synonym of -r, which means that it IS portable to use 'sed -E' to get
>> extended regular expressions in modern sed implementations, and that it
>> is no longer a GNU-only extension:

> I don't see how you can see that isn't entirely true.  As I read
> things the -E is still a proposal.  At this time no sed -E option yet
> exists in GNU sed.  

It is documented in sed.git:

$ ./sed/sed --help | grep -A1 -- -E
  -E, -r, --regexp-extended
                 use extended regular expressions in the script
                 (for portability use POSIX -E).
  -s, --separate

and exists (albeit undocumented) in older sed:

$ sed --version | head -n1
sed (GNU sed) 4.2.2
$ echo abc | sed -E 's/(b)/B/'
aBc

Hmm - that means we haven't had a sed release in quite a while; 4.2.2
came out in 2012.  Maybe this thread will spur a release.

> It certainly can't be considered portable.  Not even in bleeding edge
> systems.

I agree that it is not portable to older systems, but DOES work on
existing GNU and BSD sed implementations (even if it is undocumented in
GNU sed).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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