Inserting contents of a file with special characters using sed - bash

Question

I want to replace a marker (REPLACETHIS) in file1.txt with the entire contents of file2.txt, which will include newlines and special characters.
An example of file2.txt's contents would be
<Location />
Order deny,allow
Deny from all
Allow from 1.2.3.4
Allow from 5.6.7.8
</Location>
My general code, minus handling of special characters, would look something like this:
value=$(</home/name/scripts/file2.txt)
sed -i -e "s|REPLACETHIS|$value|" /home/name/scripts/file1.txt
What's the best way to go about handling this?

Answer 1

In sed, the best option for inserting text from file would be to use the r file command:
sed -i -e '/REPLACETHIS/{r /path/to/file2.txt' -e ';d;}' file1.txt
or, in the expanded form:
sed -i '/REPLACETHIS/ {
r /path/to/file2.txt
d
}' file1.txt
The r file command will read the text from file and insert it into the output stream. To also delete the REPLACETHIS text, we need the delete d command (heads-up: this will delete the complete line containing the text REPLACETHIS; if you need to use a mid-text marker, you could replace the d with s///, as noted by #ghoti).
In the first example, we had to break the sed program in two expressions, the reason being that r command has to end with a newline. The alternative is to write the program in several lines, as in the expanded example.
Also note that BSD sed handles -i option differently from GNU sed. The above will work in GNU, but if you need it for BSD, you should write: -i '' instead of -i.

Answer 2

One doesn't strictly need to use sed for this at all.
file_to_change=/home/name/scripts/file1.txt
value=$(</home/name/scripts/file2.txt)
infile=$(<"$file_to_change")
tempfile=$(mktemp "$file_to_change.XXXXXX")
if printf '%s\n' "${infile//REPLACETHIS/$value}" >"$tempfile"; then
mv -- "$tempfile" "$file_to_change"
else
rm -f -- "$tempfile"
fi
This works even without sed -i (which is a nonstandard, nonportable, and incompatible between common implementations).