Pipe sed to diff

Question

I want to see the diff between a paragraph in the middle of a file and a file containing a single paragraph.

The paragraph is on line 60 of file foo, and file bar contains only that paragraph with possible minor differences.

I can extract that paragraph using sed thusly: sed -n 60,60p foo. How can I use this in diff?

The following don't work:

sed -n 60,60p foo | diff bar # diff: missing operand after `foo`
diff bar `sed -n 60,60p foo` # diff: extra operand `in`

I can do:

sed -n 60,60p foo >> tempfile; diff bar tempfile

Is there a solution that doesn't require me to store somewhere temporarily using a pipe?

Answer 1

If you use a '-' as file argument, diff will read from stdin:

  sed -n 60,60p foo | diff bar -

Answer 2

You could use process substitution:

diff bar <(sed -n 60,60p foo)

This can also be used to compare the output from two processes:

diff <(sed -n 60,60p bar) <(sed -n 60,60p foo)