Replacing nth occurence

Shell Programming and Scripting
1

Hi

My input file is like this for eg:

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

2 
echo "abc abc abc abc abc abc"|sed -e "s/abc abc/abc cba/g"
abc cba abc cba abc cba
3

Given your sample data this should work:

  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:

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

% 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 ----------

Nice :slight_smile:

4

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

Another one :):

echo 'abc abc abc abc abc abc'|
awk '{for(i=2;i<=NF;i+=2){$i="cba"}}1'
6

Or:

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

Edit: Just saw it was already posted.

7

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

8

Could you give an example?

9

eg:

val1 | val2 | val1 | val2 | val1 | val2 | val1 | val2

here i need to replace '|' with '|\n' where the occurence of '|' is divisble by 2

10

I still don't understand what exactly you want to match.
If Perl is acceptable:

% print 'val1 | val2 | val1 | val2 | val1 | val2 | val1 | val2' |
  perl -pe's/(\| )/$c++%2?"$1\n":$1/ge'
val1 | val2 | 
val1 | val2 | 
val1 | val2 | 
val1 | val2
11

S that was the requirment

But now in my real use it is after every 25th occurence of '|' in a line i need to place a '\n'

For eg
i have 75 occurence of '|' in a line, so i have to replace the 25th,50th and 75th occurence of '|' with '|\n'

when i used perl -pe's/(\| )/$c++%25?"$1\n":$1/ge'
it did not work

12 
perl -pe's/(\| )/++$c%25?$1:"$1\n"/ge'