Re: DEL character treated specially when preceded by a backslash when used in the RHS of the regex operator ([[ $'\177' =~ $'\\\177' ]])

[Greg Wooledge]

On Fri, Jan 17, 2014 at 08:53:07AM -0500, Chet Ramey wrote:
> On 1/17/14 8:01 AM, Greg Wooledge wrote:
> > I would expect [[ x =~ yx ]] to fail (return 1) every time. 
> 
> There is a question about the correct behavior when y == '\', since the
> backslash is special to pattern matching.  When matching a pattern or a
> regexp, do you think x =~ \x should succeed, because the backslash acts
> as an escape?

OK, I see your point.  Here are some more experiments:

imadev:~$ [[ x =~ \x ]] ; echo $?
0
imadev:~$ bs='\'
imadev:~$ [[ x =~ ${bs}x ]] ; echo $?
0
imadev:~$ [[ x =~ $'\\'x ]] ; echo $?
1

You get to decide which one(s) are bugs. ;-)

I chose the last one because $'...' is a form of quoting, and quoting
on the right hand side of =~ removes the specialness of things, which
muddies the waters greatly.  The use of $'\\...' in the original question
led me to this, which may or may not be a tangential issue.

In order to remove that issue, I would have written the original question
this way:

imadev:~$ x=x; bs='\'; [[ $x = $bs$x ]] ; echo $?
0
imadev:~$ x=$'\177'; bs='\'; [[ $x = $bs$x ]] ; echo $?
1