sed: insert a string after every N lines

Question

I want to insert a string after every 30 lines in my large file. I\'m using mini-sed, which doesn\'t support ~ (tilde) range operator. I\'m looking for sed-only solution please.

Answer 1

This thread is another example of how to over complicate things. This should do it:

sed '0~30 s/$/string/g' < inputfile > outputfile

Every 30 lines "string" is inserted at the end of the line. If you want a new line with the word "string" just use "\n string".