No new line

gistfile1.txt

## This works as I wish (append to EOL)
→ echo -n "foo bar baz" >> out; echo -n "EOL" >> out; cat out; rm out
foo bar bazEOL

## Q: What in this `sed` causing a new line?
→ echo -n "foo bar baz" | sed "s/ /\&/g" >> out; echo -n "EOL" >> out; cat out; rm out
foo&bar&baz
EOL

## A: `sed`. 
## From the `sed` manpage: "Normally, sed cyclically copies a line of input, not including its terminating newline character, into a pattern space, (unless there is something left after a ``D'' function), applies all of the commands with addresses that select that pattern space, copies the pattern space to the standard output, appending a newline, and deletes the pattern space."
## I used a simple `awk` program to clean up after `sed`
## (`echo` text updated to be more representative of the actual input which identified the problem)

echo -n "outlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfj

outlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfj

outlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfj" \
| awk '{ORS=""; gsub("dfl", "REPLACEMENT"); if (NR!=1) print "\n"; print;}' >> out; \
echo -n "FINAL_CHARACTER" >> out; \
cat out; rm out;

The first echo example wasn't quite representative of the actual output. The actual output had newlines that I wanted to keep. It's only the last newline (the one added by sed) that I want to replace

echo -n "outlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfj

outlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfj

outlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfjoutlaksdjfl;aksjdfl;aksjdfl;kajsd;kdfjals;kdfjal;skjdf;laskjdfl;aksjdfl;kajsdfl;kajsdfl;kjas;ldfkjaslkdfjla;skjdfl;aksjdfl;aksjdfl;kasjdfl;kajsdf;lkajsd;flkjas;ldkfjas;lkdfja;lskdjf;alskdfj" \
| sed "s/dfl/REPLACEMENT/g" \
| awk '{ORS=""; if (NR==1) print; else print "\n" $0;}' >> out; \
echo -n "FINAL_CHARACTER" >> out; \
cat out; rm out;

awk was the answer.

I set the output record separator (ORS, normally \n) to an empty string (which would cause all the lines to run together).

Then, if it's the first line I print it (without the newline). For all others, I print a newline first then the line (without the newline).

That way, I can append to the end of the line as opposed to a new one

I just realized the awk program can be shortened to awk '{ORS=""; if (NR!=1) print "\n"; print;}'

Only print newlines (before the input line) for those lines greater than 1.

It turns out there's no reason to even call sed. If gsub("dfl", "REPLACEMENT"); is added to the awk program, the desired results are achieved using only one program.