[tpm] New Regex question
cj at enersave.ca
Sun Oct 28 11:23:33 PDT 2012
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.
Chapman states that \1 is used with in the pattern and $1 is used
everywhere else. He offers this example:
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;
Christopher Jones, P.Eng.
Suite 1801, 1 Yonge Street
Toronto, ON M5E1W7
email cj at enersave.ca
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