Insert line to all files when missing
In this case to turn on comments in all posts for this blog
All files that don’t have comments at the start of a line get “comments: true” inserted on the 5th line
for f in * ; do grep -q "^comments" $f || sed -i '5 i\
comments: true' $f ; done
Maybe Octopress has a way to globally enable comments - but I didn’t find it and this was quick