Use the contents of a file to replace a string using SED

Question

You can use the r command. When you find a ‘fox’ in the input…

/fox/{

…replace it for nothing…

    s/fox//g

…and read the input file:

    r f.html
}

If you have a file such as:

$ cat file.txt
the
quick
brown
fox
jumps
over
the lazy dog
fox dog

the result is:

$ sed '/fox/{
    s/fox//g
    r f.html
}' file.txt
the
quick
brown

    </div>
  </div>
  <br>
  <div id="container2">
    <div class="question" onclick="javascript:show('answer2')";>
jumps
over
the lazy dog
 dog
    </div>
  </div>
  <br>
  <div id="container2">
    <div class="question" onclick="javascript:show('answer2')";>

EDIT: to alter the file being processed, just pass the -i flag to sed:

sed -i '/fox/{
    s/fox//g
    r f.html
}' file.txt

Some sed versions (such as my own one) require you to pass an extension to the -i flag, which will be the extension of a backup file with the old content of the file:

sed -i.bkp '/fox/{
    s/fox//g
    r f.html
}' file.txt

And here is the same thing as a one liner, which is also compatible with Makefile

sed -i -e '/fox/{r f.html' -e 'd}'

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