Escaping Single-Quotes in sed

This is a just a re-post of this excellent article by Stuart Coleville:

Using single quotes in BASH ensures that the shell doesn’t expand the contents of the quoted string and this is useful most of the time. However if you want to use single quotes within a single quoted string things don’t work out as you might expect.

If I want to use sed to match some text with a single quotes in it, I will run into trouble if I run:

sed 's/user \= 'root/user \= 'moi/g'

Alternatively if I run (on the same snippet):

sed 's/user \= \'root/user \= \'moi/g'

I will get:

/bin/bash: -c: line 1: unexpected EOF while looking for matching `''
/bin/bash: -c: line 2: syntax error: unexpected end of file

This doesn’t work because the escaped single-quotes (\') are not expanded and are therefore treated literally.

To single quotes work you need to break out of the single quoted string then escape your single quote. Like so:

sed 's/user \= '\''root/user \= '\''moi/g'

Because \' is not inside of single quotes the single-quote is properly escaped and the output is as we’d expect:

user = 'root' ->  user = 'moi'

In conclusion, the title of this post is a bit of a misnomer. You actually can’t put single quotes inside of a single-quoted string. However breaking out allows us to get to where we want to be.