How do I escape a single quote in Ruby?

Question

I am passing some JSON to a server via a script (not mine) that accepts the JSON as a string.

Some of the content of the JSON contains single quotes so I want to ensure that any single quotes are escaped before being passed to the script.

I have tried the following:

> irb > 1.9.3p194 :001 > x = "that's an awesome string" >  => "that's an awesome string"  > 1.9.3p194 :002 > x.sub("'", "\'") >  => "that's an awesome string"  > 1.9.3p194 :003 > x.sub("'", "\\'") >  => "thats an awesome strings an awesome string" 

but can't seem to get the syntax right.

Answer 1

The reason sub("'", "\'") does not work is because "\'" is the same as "'". Within double quotes, escaping of a single quote is optional.

The reason sub("'", "\\'") does not work is because "\\'" expands to a backslash followed by a single quote. Within sub or gsub argument, a backslash followed by some characters have special meaning comparable to the corresponding global variable. Particularly in this case, the global variable $' holds the substring after the last matching point. Your "\\'" within sub or gsub argument position refers to a similar thing. In order to avoid this special convention, you should put the replacement string in a block instead of an argument, and since you want to match not just one, you should use gsub instead of sub:

gsub("'"){"\\'"} 

Answer 2

Why aren't you using the JSON gem?

require 'json' some_object = {'a string' => "this isn't escaped because JSON handles it.", 'b' => 2}  puts some_object.to_json => {"a string":"this isn't escaped because JSON handles it.","b":2} 

And a round-trip example:

require 'pp' pp JSON[some_object.to_json] => {     "a string" => "this isn't escaped because JSON handles it.",         "b" => 2 } 

And an example with double-quotes:

some_object = {   'a string'       => "this isn't escaped because JSON handles it.",   'another string' => 'double-quotes get "escaped"' } puts some_object.to_json => {             "a string" => "this isn't escaped because JSON handles it.",       "another string" => "double-quotes get \"escaped\""   }