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grep option "-i" does not work for me with backreference

From: Clifford Ekholm OOK
Subject: grep option "-i" does not work for me with backreference
Date: Sun, 29 Oct 2000 01:18:11 +0300 (EEST)


"grep --version" gave
grep (GNU grep) 2.4.2

Trying to learn a bit about regular expressions and tried the following to
find doubled words in a textfile that looked like this:

  Line 0: ...... Hello there.
  Line 1: ... hupa hupa ...
  Line 2: ... Hupa Hupa ...
  Line 3: ... Hupa hupa ... 
  Line 4: a b cd efg

With "egrep -i '\<([a-z]+) +\1\>'"      I only cought line 1
with "egrep -i '(\<[a-zA-Z]+) +\1\>'"   I caught line 1 and 2

with "egrep -i huPa" I caught all 3 lines which shows the option "-i" does
something; "egrep huPa" did not catch any line.

I would have thought I could have caught " Hupa hupa " even with the first

Best regards


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Clifford Ekholm                <- WWW:   http://noon.abo.fi/~cliffa/
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print +(split(//,'Just another Polack,'))[0..13,10..11,15,4,9,16..18,10,11,19];

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