Using sed, how can I replace a line containing a pattern with contents from another file?

Question

input_file.txt:

one fffds
two xxxx
three ffff
four ffde

data_file.txt:

six
seven

I want to replace the line containing two xxxx in input_file.txt with the content of data_file.txt. The output file should look like this:

output_file.txt:

one fffds
six
seven
three ffff
four ffde

Answer 1

This works for me:

sed -n '
  /two xxxx/{
    rdata_file.txt
    d
  }
  p'

If the line matches the expression, the content of the file is printed and the next cycle is started. Otherwise, the second command is invoked that prints the line.

A bit more readable solution doing a similar thing in Perl:

perl -pe '/two xxxx/ and $_=`cat data_file.txt`'