Echo or preview text changed using sed -i

Question

Using sed you can easily change text in multiple files, eg:

 sed -i 's/cashtestUS/cheque_usd/g' *.xml

The problem is that this has tremendous power, and a complex regular expression could easily have unforeseen consequences.

Is there a simple way to do either:

1) Echo the changes made
2) Run sed in a preview mode, so that the potential changes can be previewed

Answer 1

Run in preview mode without the -i:

sed -e 's/cashtestUS/cheque_usd/g' *.xml

(The -e is not necessary; it just says the next argument is the sed script, or one part of the sed script.) This writes all the output to standard output. You'd probably pipe it through less (or more), or pass it through grep to see that the changed lines were those you expected. Or you might process one file at a time and run a difference:

for file in *.xml
do
    echo "$file"
    sed -e 's/cashtestUS/cheque_usd/g' "$file" | diff -u "$file" -
done

Or …