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Re: RFE: request for quotes as grouping operators to work in brackets as


From: Chet Ramey
Subject: Re: RFE: request for quotes as grouping operators to work in brackets as elsewhere.
Date: Fri, 17 Sep 2010 22:19:51 -0400
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:1.9.2.8) Gecko/20100802 Lightning/1.0b2 Thunderbird/3.1.2

On 9/17/10 6:50 PM, Linda Walsh wrote:
> 
> 
> Jan Schampera wrote:
>> == is the same as =, my suggestion is to NOT touch that. 
> ===

I'm not going to say too much on this.  The behavior as it exists now
is very consistent: for both == and =~, any part of the rhs that's quoted
is matched as a string.  Period.  It was a mistake not to do it that
way in the first place.

Matching is different from word expansion.  The word expansions that
take place in double-quoted words on the rhs of == and =~ are the same.

I really don't understand a lot of Ms. Walsh's argument.  I appreciate
the effort she's put into this, but none of the examples she presents
demonstrate what I think she's trying to prove.

> Single quotes do not allow expansion of
> variables, double quotes do expansion of variables.  I.e.
> 
> A. t='one two three'
> a='two'
> 1) if [[ $t == 'one $a three']]; then echo 'no match expected'; fi
> 2) if [[ $t == "one $a three"]]; then echo 'Matches'; fi
> 3) if [[ $t == one\ $a\ three ]]; then echo 'Matches'; fi
> 
> So for =/==, double quotes allows *grouping* and is equivalent to 3.
> But for the =~, it is broken:
> 
> B.
> t='one two three'
> a='t..'
> 1) if [[ $t =~ 'one $a three' ]]; then echo 'no match expected'; fi
> 2) if [[ $t =~ "one $a three" ]]; then echo 'SHOULD Match'; else echo 'BUG,
> double quotes disable match'; fi
> 3) if [[ $t =~ one\ $a\ three ]]; then echo 'Matches'; fi

You realize these two cases are not equivalent, right?  Why would you
expect A2 and B2 to be treated the same when one's a string and one's
a pattern?

> 
> -- but even more of the badness, single quotes disable matching entirely:
> 4) if [[ $t =~ one\ t..\ three ]]; then echo 'Matches'; fi
> 5) if [[ $t =~ 'one t.. three' ]]; then echo 'SHOULD Match'; else echo
> 'BUG, double quotes disable match'; fi

More precisely, quoted characters are matched as strings, with any
special matching significance removed.

>   Or another disparity:  C.
> t='one two three'
> c='one two three'
> 1) if [[ $t == $a ]]; then echo 'Matches'; fi
> 2) if [[ $t == "$a" ]]; then echo 'Matches'; fi
> So, the expressions match whether or not $a is in double quotes or not

Of course they do.  They're the same string (I'm assuming that the
assignment to `c' was a typo).  There's no pattern matching happening
at all.

> (single quotes would not match, as the $a would be taken literally).
> 
> But, with the operator that says 'take right hand expression as 'RE', do we
> get consistent behavior?:
> t='one two three'
> a='one t.. three'
> 3) if [[ $t =~ $a ]]; then echo 'Matches'; fi
> 4) if [[ $t =~ "$a" ]]; then echo 'SHOULD Match'; else echo 'BUG, double
> quotes disable match'; fi
> Now, double quotes Don't behave consistently -- AGAIN....

Again, the examples are not equivalent.  Did you do this deliberately?
You're not helping your argument any by using examples that can at best
be considered disingenuous and at worst deliberately misleading.

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



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