Re: sed numbered fields don't start from parenthesis

Eric Blake <[email protected]> Thu, 02 Oct 2014 06:53:21 -0600

Newsgroups	gmane.comp.gnu.utils.bugs
Organization	Red Hat, Inc.
Message-ID	<[email protected]>

On 10/02/2014 06:41 AM, blind Pete wrote:
> Hi, 
> 
> I believe that the output from the following should be "Sep", not
> "28th_Sep".  The result can be changed by adding a ".*" to the 
> start of the search string, but I don't think that that should be 
> necessary.  Removing the trailing ".*" also produces odd results.  

Sorry, but the behavior you see is mandated by POSIX, and not a bug.

> 
> Using Ubuntu 12.04 LTS. 
> 
> $ echo 28th_September_2014 | sed "s/\(sep\).*/\1/i"

The s/// command has two steps: first, find the matching portion of the
entire line:

28th_September_2014
     ^^^^^^^^^^^^^^

then replace the portion of the line that matched with the substitution
string:

28th_Sep

You _do_ have to use .* on both front and end of the pattern if you want
to shorten an entire line down to just a matched backref number.

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

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