Double loop over files for better performance

double-xargs.sh

# Assumes two files present (`sel` and `filez`)
# OSX needs an empty zero length argument, which is quite difficult to escape if using the same type of quotations
# Inner file (`filez`) is used over a `find ... -exec` to cut down on repetitive operations
cat sel | xargs -I '{}' sh -c 'cat filez | xargs sed -i "" "s/{}//"'