Concise and portable “join” on the Unix command-line

Question

How can I join multiple lines into one line, with a separator where the new-line characters were, and avoiding a trailing separator and, optionally, ignoring empty lines?

Answer 1

Perhaps a little surprisingly, paste is a good way to do this:

paste -s -d","

This won't deal with the empty lines you mentioned. For that, pipe your text through grep, first:

grep -v '^$' | paste -s -d"," -