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Replacing nth occurence


 
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# 1  
Old 10-29-2009
Replacing nth occurence

Hi

My input file is like this for eg:
Code:
abc abc abc abc abc abc

i would like to replace "abc" with "cba" where the occurrence is divisible by 2

of eg here 2nd, 4th and 6th occurence shud be replace

can anyone suggest in awk or sed

Last edited by zaxxon; 10-29-2009 at 10:35 AM.. Reason: use code tags please
# 2  
Old 10-29-2009
Code:
echo "abc abc abc abc abc abc"|sed -e "s/abc abc/abc cba/g"
abc cba abc cba abc cba


Last edited by Franklin52; 10-29-2009 at 10:45 AM.. Reason: Please use code tags!
# 3  
Old 10-29-2009
Given your sample data this should work:

Code:
  awk '{ for (i=1; i<=NF; i++)
           $i = i % 2 ? $i : "cba"
        }1'

Be aware that the above code will squeeze consecutive FS characters.

With Perl:

Code:
perl -pe's/(\w+)/$c++%2?cba:$1/ge'

Code:
% print abc abc abc abc abc abc |
  awk '{ for (i=1; i<=NF; i++)      
           $i = i % 2 ? $i : "cba"
        }1'
abc cba abc cba abc cba
% print abc abc abc abc abc abc |
  perl -pe's/(\w+)/$c++%2?cba:$1/ge'
abc cba abc cba abc cba



---------- Post updated at 02:45 PM ---------- Previous update was at 02:45 PM ----------

Quote:
Originally Posted by methyl
Code:
echo "abc abc abc abc abc abc"|sed -e "s/abc abc/abc cba/g"
abc cba abc cba abc cba

Nice Smilie
# 4  
Old 10-29-2009
Hi thax for the reply but im making an example since in my requirements its 25rd every occurence i need to replace in a line
# 5  
Old 10-29-2009
Another one Smilie:

Code:
echo 'abc abc abc abc abc abc'|
awk '{for(i=2;i<=NF;i+=2){$i="cba"}}1'

# 6  
Old 10-29-2009
Or:

Code:
awk '{ 
  for (i=2; i<=NF; i+=2) 
    $i = "cba"
        }1'

Edit: Just saw it was already posted.
# 7  
Old 10-29-2009
Thanks for the reply i need to match "abc" within other patterns also
like
abc bbb bbb abc bbb ccc abc
so need to match the pattern and occurence too

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