How to escape the ampersand character while using sed

Question

I want to replace all single quotes in a string with two single quotes using sed. But when the string contains the & character, the sed command is not replacing single quotes that come after that. How can I escape the & character so that the single quotes after it are still replaced?

Answer 1

You don't need to escape anything in the input:

$ echo "123 ' foo & b'ar" | sed "s/'/''/g"
123 '' foo & b''ar

However, in the 'replacement' part of the s command & has a special meaning: it means 'match'. That's why the above command can be re-written as:

$ echo "123 ' foo & b'ar" | sed "s/'/&&/g"
123 '' foo & b''ar

Escape it with a \ like everything else that needs to be escaped, if needed:

$ echo "123 ' foo & b'ar" | sed "s/'/'\&'/g"
123 '&' foo & b'&'ar

Answer 2

It's easier to answer if you post your code, but I'm guessing you're not escaping the ampersand. Change & to \& if you want a literal ampersand.

See section 3.1.2 of The sed FAQ for a more detailed explantion, if you're curious.