Ruby WTF? Escaping single quotes in Ruby using gsub

I’m currently working on a project which requires me to escape JavaScript (don’t ask why). To get it working, I had to escape single quotes. I was encountering weird behavior in my code, so I ran the following in IRB.

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2.2.1 :002 > "Doesn't work".gsub("'", "\\'")
 => "Doesnt workt work"

WAT.

I did a bit of investigation (read: Stack Overflow) and found that \' is a special escape sequence in the gsub replacement – it’s a backreference that represents $', the characters that match after the single quote.

In order to fix this bug, you must escape the backslash within gsub as so:

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2.2.1 :003 > "Doesn't work".gsub("'", "\\\\'")
 => "Doesn\\'t work"

Nota bene: The double backslash returned by IRB is actually a single escaped backslash – it hasn’t generated another one.

gsub first escapes everything as a Ruby string, then it parses the result of that string as a regex. It’s not documented well at all – I couldn’t find anything on this in the documentation.

Ruby’s such a weird language.