replace every second occurance of a string

ratheeshjulk · November 10, 2011, 3:26am

I want to replace every 2nd occurance of a string/character from a line.

ababacbsbddbsbbcbdbssb

i want to replace every s2nd b with @ like below
should be like

aba@acbs@ddbs@bc@dbss@

itkamaraj · November 10, 2011, 3:27am

what you tried so far ?

ratheeshjulk · November 10, 2011, 3:32am

awk '/b/{c++;if(c%2=0){sub("b","@");c=0}}1' file1 > file2

suppose the string is present in the file1 and write to file2

itkamaraj · November 10, 2011, 3:43am

echo "ababacbsbddbsbbcbdbssb" | nawk -Fb '{for(i=1;i<=NF;i++){if(i%2==1){printf("%sb",$i)}else{printf("%s@",$i)}}}'