Is is possible to create a string in ruby that keeps escaping characters?

Question

I need to form a user-data script from Ruby so I need all escaping characters to remain. When I do this:

  def user_data
     "#!/bin/bash
     sed -i -e '/<Name>loadbalanceServerIP<\/Name>/,/<Value>/s/<Value>[^<]*/<Value>1.1.1.1/' /home/wowza/conf/Server.xml"
  end

The string removes the \ in the Name tag. If I put two \, it keeps them both. Any suggestion as how to keep the string the same way I wrote it?

Thank you!

It's correct ruby behaviour. When you puts your string with double \, you will see only one. — Dmitry Z., Nov 16 '16 at 15:33
@LeticiaEsperon no, it doesn't. It _shows_ two backslashes when you are inspecting the string, but the string contains only one backslash: `"\\".size #=> 1` — Stefan, Nov 16 '16 at 15:50
Oh!! That's right. Thank you very much, that was the information I was lacking. — Leticia Esperon, Nov 16 '16 at 16:02
I'd recommend reading http://stackoverflow.com/q/8554479/128421 and https://en.wikipedia.org/wiki/Escape_character. This is well documented behavior. — the Tin Man, Nov 16 '16 at 16:09
I am not able to reproduce your problem: `"\\".length #=> 1`. Which version of Ruby are you using? Which implementation? How *exactly* are you constructing your `String`? Is it a literal? Does it come from somewhere else? Do you parse it? Generate it? Could there be a double parsing or double escaping bug somewhere in your code? — Jörg W Mittag, Nov 16 '16 at 16:12
This question is different. The OP wants to enter / keep a multi-line string containing `'` and ``\`` (literally) as-is, without having to specifically quote anything. — Stefan, Nov 16 '16 at 16:14

score 1 · Accepted Answer · answered Nov 16 '16 at 15:41

1

You can use the %q delimiter rather than ":

def user_data
     %q[#!/bin/bash
     sed -i -e '/<Name>loadbalanceServerIP<\/Name>/,/<Value>/s/<Value>[^<]*/<Value>1.1.1.1/' /home/wowza/conf/Server.xml]
end

answered Nov 16 '16 at 15:41

ReggieB

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If I do that in Rails console it puts <\\/Name> – Leticia Esperon Nov 16 '16 at 15:46
`"` is used to define the string. The string starts `"#!/bin/bash ...` and ends on the next line with `....Server.xml"` – ReggieB Nov 16 '16 at 15:47
It show that as the property of the string, but if you output it for (example `puts %q[<\/Name>]`) it will be formatted correctly – ReggieB Nov 16 '16 at 15:49
Sorry, I didn't understand. The output of that code is .......<\\/Name>........ – Leticia Esperon Nov 16 '16 at 15:50
Really? `puts %q[<\/Name>]` outputs `<\/Name>` – ReggieB Nov 16 '16 at 15:54
I meant in the rails console without using puts. But you are right. The thing was I dind't know that it was showing two backslashes but they were actually just one!! – Leticia Esperon Nov 16 '16 at 16:03

score 0 · Answer 2 · answered Nov 16 '16 at 16:05

I'd use a heredoc:

def user_data
  <<~'SH'
    #!/bin/bash
    sed -i -e '/<Name>loadbalanceServerIP<\/Name>/,/<Value>/s/<Value>[^<]*/<Value>1.1.1.1/' /home/wowza/conf/Server.xml
  SH
end

puts user_data

~ removes the indentation, and the single quotes around SH disable interpolation and escaping.

Output:

#!/bin/bash
sed -i -e '/<Name>loadbalanceServerIP<\/Name>/,/<Value>/s/<Value>[^<]*/<Value>1.1.1.1/' /home/wowza/conf/Server.xml

Is is possible to create a string in ruby that keeps escaping characters?

2 Answers2