How to replace newline with space except when it's the only character in a row

Question

I have some text like:

from her patient
scrutiny
and judicious criticism.

J.K.

WASHINGTON, D.C.

April, 1919.

And want to leave it like:

from her patient scrutiny and judicious criticism.

J.K.

WASHINGTON, D.C.

April, 1919.

How can I do it? I know you can replace newlines easily using the find & replace tool with /r/n but I don't know how to do this.

Some extra step: I also want to delete one newline if the previous line was empty and just had a newline character. Is that possible?

I don't know much about programming but I'm okay if I need to use bash or any Terminal tool to do this. However I hope I can use 4 cpu cores because the text file is really long.

Answer 1

• Ctrl+H
• Find what: (?<=\S)\R(?=\S)
• Replace with: # a space
• check Wrap around
• check Regular expression
• Replace all

Explanation:

(?<=\S)     # positive lookbehind, make sure we have a NON space character before
\R          # any kind of line break
(?=\S)      # positive lookahead, make sure we have a NON space character after

Result for given example:

from her patient scrutiny and judicious criticism.

J.K.

WASHINGTON, D.C.

April, 1919.

Screen capture: