Make a string both valid JSON and shell escaped - json

Question

I have an array which I want to convert to a JSON string. One of the elements has a backtick. This would cause an error when I try to run the command in the shell:
data = [["305", "John Smith", "Amy Smith`", "10/11/2008", "Medical", {"page_count"=>4}]]
json_str = data.to_json.gsub('"','\"')
cmd = "node myscript.js #{json_str}"
Open3.popen3(cmd) do |stdin, stdout, stderr, wait_thr|
output = [stdout.read, stderr.read]
end
Error retrieving data: sh: 1: Syntax error: EOF in backquote substitution
An obvious solution is to escape the backtick:
json_str = data.to_json.gsub('"','\"').gsub('`','\\\`')
But I want to escape all special shell characters that could raise an isuse. Ruby's shellescape escapes a string so that it can be safely used in a Bourne shell command line. Here's an example:
argv = "It's better to give than to receive".shellescape
argv #=> "It\\'s\\ better\\ to\\ give\\ than\\ to\\ receive"
But look what happens when I apply it to JSON string:
data = [["305", "John Smith", "Amy Smith`", "10/11/2008", "Medical", {"page_count"=>4}]]
data = data.to_json
=> "[[\"305\",\"John Smith\",\"Amy Smith`\",\"10/11/2008\",\"Medical\",{\"page_count\":4}]]"
data = data.to_json.shellescape
=> "\\"\\\\"\[\[\\\\\\\\"305\\\\\\\\",\\\\\\\\"John\ Smith\\\\\\\\",\\\\\\\\"Amy\ Smith\`\\\\\\\\",\\\\\\\\"10/11/2008\\\\\\\\",\\\\\\\\"Medical\\\\\\\\",\{\\\\\\\\"page_count\\\\\\\\":4\}\]\]\\\\"\\""
Clearly, this would raise an error like:
SyntaxError: Unexpected token \ in JSON at position 0
What happens is that shellescape will also escape spaces, since the shell requires spaces to be escaped. But having spaces is valid and necessary JSON. So how could I escape shell characters that would cause an error in my command without it breaking the JSON?

Answer 1

Shells are for humans, not for machines. Having a machine produce shell commands is a code smell indicating that you're automating at the wrong layer.
Skip the shell, and just run your program with the required arguments:
data = [["305", "John Smith", "Amy Smith`", "10/11/2008", "Medical", {"page_count"=>4}]]
json_str = data.to_json
Open3.popen3("node", "myscript.js", json_str) do |stdin, stdout, stderr, wait_thr|
output = [stdout.read, stderr.read]
end
Since there is no shell involved, there's no human silliness like escaping to care about.