[tpm] New Regex question

[Rob Janes]

I suspect Chris is on linux/unix, reading \r\n.  that conversion from \r\n
to \n would only happen on a windows perl, reading a windows text file.
it's not clear such a conversion would happen even in windows perl if it
was reading a database blob (or whatever it was), which is what Chris is
doing.

On Sun, Oct 28, 2012 at 2:44 PM, Tom Legrady <legrady at gmail.com> wrote:

>
>
> On Sun, Oct 28, 2012 at 2:23 PM, Chris Jones <cj at enersave.ca> wrote:
>
>> At 07:22 PM 27/10/2012, Uri Guttman wrote:
>>
>>> On 10/27/2012 06:57 PM, Rob Janes wrote:
>>>
>>>> $1 doesn't work.
>>>>
>>>> \1 is the characters matched while $1 is the pattern matched.
>>>>
>>>> It only matters if u want to match pure string.
>>>>
>>>
>>> that is wrong. both are only references to a grab which is always a
>>> string. you can use \1 in the regex to match what you have previously
>>> matched and grabbed. $1 is used in the replacement or after the regex to
>>> get what was grabbed. neither contains a regex.
>>>
>>> uri
>>>
>>
>> Chapman states that \1 is used with in the pattern and $1 is used
>> everywhere else.  He offers this example:
>>
>> while(<>)
>> {
>>    s/(\w+ and \1/$1 twice/;
>>    s/(w+) and (\w+)/$2 and $1/;
>> }
>>
>> This example reverses pairs of different words, 'Marks and Spencer' into
>> 'Spencer and Marks', and collapses identical pairs, taking 'Sattchi and
>> Sattchi' into 'Sattchi twice'
>>
>> So, my example should be $exp =~ s/(\s|\r\n)\1+/$1/g;
>>
>
> You don't need \r\n ... \n is sufficient:
>
>       "\n matches a logical newline. Perl converts between \n and your
>        OS's native newline character when reading from or writing to text
>        files."
>                   'Character Escapes'
>                   in http://perldoc.perl.org/perlrebackslash.html
>
> Also, do you want to wind up with either a space or a newline,
> accidentally, depending on which one came first?
>
> Consider       "line 1 \n \nline 3" collapsing into "line1 line 3"
> compared to "line 1\n \nline 3"  collapsing into "line1\nline 3"
> just because of a trailing  space.
>
> Tom
>
>
>> >>
>> Christopher Jones, P.Eng.
>> Suite 1801, 1 Yonge Street
>> Toronto, ON M5E1W7
>> Tel. 416-203-7465
>> Fax. 416-946-1005
>> email cj at enersave.ca
>>
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>
>
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