BASH: insert text in a specific position

Question

I would like to find a solution to add some characters in a string

Example

folder/dir/directory/file.txt
shares/page.html
etc/downloads/torrent.torrent

Should become

.folder.old/dir/directory/file.txt
.shares.old/page.html
.etc.old/downloads/torrent.torrent

How can i do that? 'grep' would be a correct choose?

Thank you

Answer 1

Use sed instead of grep:

sed -i.bak 's#^\([^/]*\)#.\1.old#'

Note that -i will save the result in the original file itself. -i.bak will save your original file with .bak extension in case something goes wrong.