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:
paulo:~$ re='\<foo\>'
paulo:~$ [[ 'foo bar' =~ $re ]] && echo yes || echo no
yes
paulo:~$ [[ 'foobar' =~ $re ]] && echo yes || echo no
no
It baffles me that literal \< \> are not evaluated correctly
paulo:~$ [[ 'foo bar' =~ \<foo\> ]] && echo yes || echo no
no
This indicates that bash also recognizes \b as word anchor:
paulo:~$ re='\bfoo\b'
paulo:~$ [[ 'foo bar' =~ $re ]] && echo yes || echo no
yes
paulo:~$ [[ 'foobar' =~ $re ]] && echo yes || echo no
no
but it also baffles me literal \b is not evaluated correctly:
paulo:~$ [[ 'foo bar' =~ \bfoo\b ]] && echo yes || echo no
no
Empirically all this demonstrates:
1. bash recognizes \< \> \b as word anchors
2. bash doesn't evaluate them correctly when used as literals
3. bash evaluates them correctly when used with parameter expansion
