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Re: Word boundary anchors \< and \> not parsed correctly on the right si


From: Chet Ramey
Subject: Re: Word boundary anchors \< and \> not parsed correctly on the right side of =~
Date: Tue, 10 Jul 2018 10:50:05 -0400
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.9.0

On 7/10/18 9:02 AM, Paulo Marcel Coelho Aragão wrote:
> On Tue, Jul 10, 2018 at 08:27:18AM -0400, Greg Wooledge wrote:
>> Bash uses ERE (Extended Regular Expressions) here.  There is no \< or \>
>> in an ERE.
>>
>> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04
> 
> Thanks for the reference. The document lists only ^ and $ as anchors. 
> However, this indicates to me that bash recognizes \< \> as word anchors:

No, it doesn't. It indicates that the system's POSIX regular expression
implementation has extensions.

> Empirically all this demonstrates:
> 
> 1. bash recognizes \< \> \b as word anchors

No, it doesn't.

> 2. bash doesn't evaluate them correctly when used as literals

Yes, it does. It may not conform to your assumptions.

> 3. bash evaluates them correctly when used with parameter expansion

No. It passes them to the system's POSIX regexp library function, which
understands them as an extension.


-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    address@hidden    http://tiswww.cwru.edu/~chet/



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