Substitute pattern within a file with the content of other file

Question

I have a text file (devel.xml).

I added the word REPLACETHIS to it in order to replace this string with the content within a different file (temp.txt).

The closest thing I have is this:

sed -i -e "/SUBSTITUTETHIS/r temp.TXT" -e "s///" devel.txt;

This inserts the content after the string, and then deletes the string afterwards.

Is this the best way to do it?

Answer 1

What you've done is to remove SUBSTITUTETHIS wherever it appears in the file (but not the rest of the line where it appears) and insert the content of temp.TXT below that line. If SUBSTITUTETHIS appears multiple times on a line, only the first occurrence is removed, and only one copy of temp.TXT is added.

If you want to replace the whole line when SUBSTITUTETHIS appears, use the d command. Since you need to run both r and d when there's a match, put them in a braced group.

sed -e '/SUBSTITUTETHIS/ {' -e 'r temp.TXT' -e 'd' -e '}' -i devel.txt

Some sed implementations let you use semicolons to separate commands and omit separators altogether around braces, but you still need a newline to terminate the argument to the r command:

sed -e '/SUBSTITUTETHIS/ {r temp.TXT
                          d}' -i devel.txt

If you want to replace SUBSTITUTETHIS by the content of the file, but retain what comes before and after it on the line, it's more complicated. The simplest method is to include the content of the file in the sed command; note that you'll have to properly quote its contents.

sed -e "s/SUBSTITUTETHIS/$(<temp.TXT sed -e 's/[\&/]/\\&/g' -e 's/$/\\n/' | tr -d '\n')/g" -i devel.txt

Or use Perl.

perl -pe 's/SUBSTITUTETHIS/`cat temp.TXT`/ge' -i devel.txt

Answer 2

Assuming your temp.txt file has EXACTLY what you want to replace SUBSTITUTETHIS with and nothing else:

sed -i -e "s/SUBSTITUTETHIS/`cat temp.txt`/" devel.txt