Re: Word boundary anchors \< and \> not parsed correctly on the right side of =~

[Ilkka Virta]

On 10.7. 15:27, Greg Wooledge wrote:
> On Mon, Jul 09, 2018 at 10:46:13PM -0300, marcelpaulo@gmail.com wrote:
> > Word boundary anchors \< and \> are not parsed correctly on the right side of a 
> > =~ regex match expression.
>
> Bash uses ERE (Extended Regular Expressions) here.  There is no \< or \>
> in an ERE.

Or does it use the system's regex library, whatever that supports?

On my Linux systems, this prints 'y' (with Bash 4.4.12 and 4.1.2):
re='\<foo\>' ; [[ "foo bar" =~ $re ]] && echo y


If '\<' matches just a regular less-than sign (but has a useless 
backslash), then surely that should not match?

That's the same example marcelpaulo@gmail.com had, they didn't have
the <> signs in the string.

On my Mac, the above doesn't match. The same thing with a similar regex 
with \w .

> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04
>
> > This evaluates as false:
> >
> >      [[ 'foo bar' =~ \<foo\> ]]
>
> Well, of course it does, because \< is just a literal less-than sign
> in a POSIX ERE.
>
> wooledg:~$ re='\<foo\>'
> wooledg:~$ [[ '<foo>' =~ $re ]] && echo yes
> yes
>
> You might as well remove the backslashes, because they serve no purpose
> here.  If you thought they meant "word boundary" or something, you're
> in the wrong language.


--
Ilkka Virta / itvirta@iki.fi