This problem is easily solved with a regexp that processes the input as a whole, rather than working on it line by line. I had this need often enough that I ex

This problem is easily solved with a regexp that processes the input as a whole, rather than working on it line by line. I had this need often enough that I exported Go regexp engine as a command line tool regrep, which can insert "elephant" after "baz" with: go get github.com/orivej/unix/regrep regrep s '(\n( *-) baz\n)' $'$1$2 elephant\n' < input.yaml It only processes standard input, and can not by itself replace the contents of an input file with its output; but another tool, inplace, helps: go get github.com/orivej/unix/inplace find . -name '*.yaml' -exec inplace {} regrep s '(\n( *-) baz\n)' $'$1$2 elephant\n' \;