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 repla

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