Re: [Help-bash] ${var//!([[:class:]])} removing characters of the [:class:]

[Pierre Gaston]

On Sun, Jan 27, 2013 at 11:34 AM, Mart Frauenlob
<address@hidden> wrote:
> On 27.01.2013 10:08, Pierre Gaston wrote:
>>
>> On Sun, Jan 27, 2013 at 10:46 AM, Mart Frauenlob
>> <address@hidden> wrote:
>>>
>>> On 27.01.2013 09:31, Pierre Gaston wrote:
>
> [...]
>
>>>> because inside [[:alpha:]] only matches 1 character
>>>> so abc is not match by alpha since it is 3 character, abc is the
>>>> longest string that doesn't match and it removed
>>>> you get abc with:
>>>>    x=abc;echo ${x/!(+([[:alpha:]]))}
>>>>
>>>
>>> thank you very much for that explanation!
>>>
>>> have a nice day
>>
>>
>> cool, just for completion (well ok there may be even more)about the
>> not so obvious things with !()...you should take care that the empty
>> string is also a "non-match":
>>
>> $ x=abc;echo ${x//!(+([[:alpha:]]))/r}
>> rarbrc
>>
>> each empty string before and after the chars is not matched by "one or
>> more alpha" and is replaced
>>
>
> My previous error is obvious to me now, but this one I'm not sure if I
> understand.
> Does this mean a string in bash has internally separated each character with
> a NULL char?

No, it's just that by definition the negation of "one or more thing A"
can be "thing B" but it can also be "nothing" and there is "nothing"
between each character but "nothing" is not a physical byte

in the regex world, the example of this is:
$ echo foo | sed 's/m*/a/g'
afaoaoa
Here 0 or more m matches the "nothing" between the characters

The common mistake is to think "ls *!(.jpg)" will list all the files
but the .jpg
It doesn't work, because * can match "foo.jpg" and !(.jpg) can match
the empty string after it. (ls !(*.jpg) is what should be used)