how to work with plain text

Tested in Pluma, but other text editors should work similarly:

Use "find and replace" (Ctrl+H in Pluma). Make sure "Parse escape sequences" is checked.

- replace "AM" with "AM\n\n"
- replace "PM" with "MP\n\n"
- replace "Received from" with "\n\nReceived from"

That should work in Trisquel 7's terminal (but not necessarily with another implementation of sed than a recent GNU sed):
$ sed -i -e 's/[AP]M/&\n\n/g' -e 's/Received from/\n\n&/g' file.txt

Simple example using GNU Sed:

printf '01:00AM\nReceived from Ana\n02:00 PM\n03:00 AM\nReceived from
Bob\n' | sed 's/[AP]M/\0\n\n/g; s/Received from/\n\n\0/g'

For safety purposes, sed doesn't replace the contents of the file,
unless you pass `-i' to it.

2017-12-09T23:24:47+0100 name at domain wrote:
> Hi friends
>
> I have a big plain text (.txt) file that I would like to edit in the
> following ways:
>
> 1. after every "AM" or "PM, insert two "Enter"s (line breaks .. like
> if this were HTML)
>
> 2. before every "Received from", insert two "Enter"s
>
> There might be a hundred to three hundred of these in the text file.
> Would you teach me how to do it automatically somehow?

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