How to perform String replacements without backslash escaping in Ruby

Question

Consider the code:

output = `cat test.txt`
puts output  # /^\\([0-3][0-9]\\/[0-1][0-9]\\/[2-9][0-9]{3}\\)$/
str = 'test ' + output
puts str     # test /^\\([0-3][0-9]\\/[0-1][0-9]\\/[2-9][0-9]{3}\\)$/
new_str = 'new test ' + output
puts new_str # new test /^\\([0-3][0-9]\\/[0-1][0-9]\\/[2-9][0-9]{3}\\)$/

res = str.sub('test', 'new test')
puts res     # new test /^\\([0-3][0-9]\\/[0-1][0-9]\\/[2-9][0-9]{3}\\)$/ <-- all fine
res = str.sub(str, new_str)
puts res     # new test /^\([0-3][0-9]\/[0-1][0-9]\/[2-9][0-9]{3}\)$/     <-- !!! problem

code is just for presenting the problem which I have ;)

Problem: I have replacement text with double backslashes which I need to write "as it is" to another file

Question is: is there any simple replacement method which doesn't interpret backslashes (maybe some binary mode)?

Because it's kinda weird to do like this: res = str.sub(str, new_str.gsub('\\', '\\\\\\\\')), although this works...

real working code:

file = 'some/random/file.php'
contents = new_contents = ''
File.open(file, 'rb') do |f|
  contents = new_contents = f.read
end

contents.scan(/('([A-Z]+)' \=\> \<\<\<'JSON'(.*?)JSON)/m) do |match|
  Dir.glob("*#{match[1]}.json") do |filename|
    compressed = `../compress.py #{filename}`.gsub('\\', '\\\\\\\\')
    replacement = match[0].sub(match[2], "\n" + compressed).force_encoding('ASCII-8BIT')

    new_contents = new_contents.sub(match[0], replacement.gsub('\\', '\\\\\\\\'))
  end
end

File.open(file, 'wb') do |f|
  f.write(new_contents)
end

Answer 1

Eventually I found pretty simple solution:

input = '{"regex": "/^\\\\([0-3][0-9]\\\\)$/"}'
puts input # gives => {"regex": "/^\\([0-3][0-9]\\)$/"}

search = '/^\\\\([0-3][0-9]\\\\)$/'
replace = '/^\\\\([0-9]\\\\)$/'

puts input.sub(search, replace) # gives => {"regex": "/^\([0-9]\)$/"}, which is wrong result

input[search] = replace # <-- here is the trick, but makes changes in place
puts input # gives => {"regex": "/^\\([0-9]\\)$/"} => success!

But! If your string doesn't contain any search substring you will get an string not matched (IndexError).

So you may want to bulletproof your code like this:

input[search] = replace if input.include? search

Also, if you want to keep your input untouched you may .dup it to another variable:

new_input = input.dup
new_input[search] = replace if new_input.include? search

Answer 2

You can replace part of a string using a range. So you just have to find that range

if index = string.index(str_to_replace)
  string[index...(index + str_to_replace.length)] = replacement
end

This example does it in place, so do it to a dup if necessary.