Best way to escape and unescape strings in Ruby?

Question

Does Ruby have any built-in method for escaping and unescaping strings? In the past, I've used regular expressions; however, it occurs to me that Ruby probably does such conversions internally all the time. Perhaps this functionality is exposed somewhere.

So far I've come up with these functions. They work, but they seem a bit hacky:

def escape(s)
  s.inspect[1..-2]
end

def unescape(s)
  eval %Q{"#{s}"}
end

Is there a better way?

Answer 1

Ruby 2.5 added String#undump as a complement to String#dump:

$ irb
irb(main):001:0> dumped_newline = "\n".dump
=> "\"\\n\""
irb(main):002:0> undumped_newline = dumped_newline.undump
=> "\n"

With it:

def escape(s)
  s.dump[1..-2]
end

def unescape(s)
  "\"#{s}\"".undump
end

$irb
irb(main):001:0> escape("\n \" \\")
=> "\\n \\\" \\\\"
irb(main):002:0> unescape("\\n \\\" \\\\")
=> "\n \" \\"

Answer 2

There are a bunch of escaping methods, some of them:

# Regexp escapings
>> Regexp.escape('\*?{}.')   
=> \\\*\?\{\}\. 
>> URI.escape("test=100%")
=> "test=100%25"
>> CGI.escape("test=100%")
=> "test%3D100%25"

So, its really depends on the issue you need to solve. But I would avoid using inspect for escaping.

Update - there is a dump, inspect uses that, and it looks like it is what you need:

>> "\n\t".dump
=> "\"\\n\\t\""

Answer 3

Caleb function was the nearest thing to the reverse of String #inspect I was able to find, however it contained two bugs:

• \\ was not handled correctly.
• \x.. retained the backslash.

I fixed the above bugs and this is the updated version:

UNESCAPES = {
    'a' => "\x07", 'b' => "\x08", 't' => "\x09",
    'n' => "\x0a", 'v' => "\x0b", 'f' => "\x0c",
    'r' => "\x0d", 'e' => "\x1b", "\\\\" => "\x5c",
    "\"" => "\x22", "'" => "\x27"
}

def unescape(str)
  # Escape all the things
  str.gsub(/\\(?:([#{UNESCAPES.keys.join}])|u([\da-fA-F]{4}))|\\0?x([\da-fA-F]{2})/) {
    if $1
      if $1 == '\\' then '\\' else UNESCAPES[$1] end
    elsif $2 # escape \u0000 unicode
      ["#$2".hex].pack('U*')
    elsif $3 # escape \0xff or \xff
      [$3].pack('H2')
    end
  }
end

# To test it
while true
    line = STDIN.gets
    puts unescape(line)
end

Answer 4

Update: I no longer agree with my own answer, but I'd prefer not to delete it since I suspect that others may go down this wrong path, and there's already been a lot of discussion of this answer and it's alternatives, so I think it still contributes to the conversation, but please don't use this answer in real code.

If you don't want to use eval, but are willing to use the YAML module, you can use it instead:

require 'yaml'

def unescape(s)
  YAML.load(%Q(---\n"#{s}"\n))
end

The advantage to YAML over eval is that it is presumably safer. cane disallows all usage of eval. I've seen recommendations to use $SAFE along with eval, but that is not available via JRuby currently.

For what it is worth, Python does have native support for unescaping backslashes.

Answer 5

Ruby's inspect can help:

    "a\nb".inspect
=> "\"a\\nb\""

Normally if we print a string with an embedded line-feed, we'd get:

puts "a\nb"
a
b

If we print the inspected version:

puts "a\nb".inspect
"a\nb"

Assign the inspected version to a variable and you'll have the escaped version of the string.

To undo the escaping, eval the string:

puts eval("a\nb".inspect)
a
b

---

I don't really like doing it this way. It's more of a curiosity than something I'd do in practice.

Answer 6

YAML's ::unescape doesn't seem to escape quote characters, e.g. ' and ". I'm guessing this is by design, but it makes me sad.

You definitely do not want to use eval on arbitrary or client-supplied data.

This is what I use. Handles everything I've seen and doesn't introduce any dependencies.

UNESCAPES = {
    'a' => "\x07", 'b' => "\x08", 't' => "\x09",
    'n' => "\x0a", 'v' => "\x0b", 'f' => "\x0c",
    'r' => "\x0d", 'e' => "\x1b", "\\\\" => "\x5c",
    "\"" => "\x22", "'" => "\x27"
}

def unescape(str)
  # Escape all the things
  str.gsub(/\\(?:([#{UNESCAPES.keys.join}])|u([\da-fA-F]{4}))|\\0?x([\da-fA-F]{2})/) {
    if $1
      if $1 == '\\' then '\\' else UNESCAPES[$1] end
    elsif $2 # escape \u0000 unicode
      ["#$2".hex].pack('U*')
    elsif $3 # escape \0xff or \xff
      [$3].pack('H2')
    end
  }
end

Answer 7

I suspect that Shellwords.escape will do what you're looking for

https://ruby-doc.org/stdlib-1.9.3/libdoc/shellwords/rdoc/Shellwords.html#method-c-shellescape