MongoDB - strip non numeric characters in field

You'll have to iterate over all your docs in code and use a regex replace to clean up the strings.

Here's how you'd do it in the mongo shell for a test collection with a phone field that needs to be cleaned up.

db.test.find().forEach(function(doc) {
  doc.phone = doc.phone.replace(/[^0-9]/g, ''); 
  db.test.save(doc);
});

Based on the previous example by @JohnnyHK, I added regex also to the find query:

/*
MongoDB: Find by regular expression and run regex replace on results
*/
db.test.find({"url": { $regex: 'http:\/\/' }}).forEach(function(doc) {
  doc.url = doc.url.replace(/http:\/\/www\.url\.com/g, 'http://another.url.com'); 
  db.test.save(doc);
});