Sed: Append file to end of line

Sed can let you replace part of a line with new content from another file. This is how I do this in three steps. You can see the code run a codingground

By using a file to insert the replacement text the content can contain special characters that would normally require a lot of extra work to escape. 

#!/bin/bash

# Replace the right portion of a line with the content of a file.
# 1) Replace the right portion of a line with a marker word
# 2) Append after the marker with the content from a file
# 3) Remove the marker and new line to pull the next line up.

cat > outfile <<!EOF
hello there tom
        How are you today?
    Where is the dog show?
!EOF

cat outfile

cat > testfile <<!EOF
flowers doing?
!EOF


sed -i outfile -e 's/you.*/REPLACE_MARKER/g'
printf "\n\n\n"
cat outfile

sed -i outfile -e "/REPLACE_MARKER/r testfile"
printf "\n\n\n"
cat outfile

sed -i outfile -e "/REPLACE_MARKER/{:a;N;s/REPLACE_MARKER\n//}"
printf "\n\n\n"
cat outfile