Question

I have a simple text file with content:

   patent-inv

I’m going to replace patent-inv with part1\\part2

I did it in such way:

source_file = IO.read("#{Rails.root}/my_userdata/1.txt")
source_file.gsub!('<<<patent-inv>>>', "part1\\\\part2")             
File.open("#{Rails.root}/my_userdata/2.txt", "wb") {|f| f.write source_file }

But in file I got:
part1\part2

I tried several ways, but I got the same result:

source_file.gsub!('<<<patent-inv>>>', "part1\\\\part2") => "part1\part2"
source_file.gsub!('<<<patent-inv>>>', "part1\\\part2") => "part1\part2"
source_file.gsub!('<<<patent-inv>>>', "part1\\part2") => "part1\part2"

Could Anyone help me find out this strange behavior?

Answer 1

The following works for me. Have you tried it in the terminal? It could be unescaped when you output the result.

> a = "<<<patent-inv>>>"
> a.gsub("<<<patent-inv>>>", "part1\\\\part2")    
=> "part1\\part2" 

You can see how the output varies between puts and p

> puts a
part1\part2
> p a
"part1\\part2"
> puts a.inspect
"part1\\part2"

EDIT Here is the output displayed as you want it.

1.9.2-p290 :037 > a.gsub!("<<<patent-inv>>>", "part1\\\\\\part2")
 => "part1\\\\part2" 
> p a
"part1\\\\part2"
 => "part1\\\\part2" 
> puts a
part1\\part2
 => nil 

We know that 4 backslashes when changed equals 2 backslashes when unescaped. So 4 backslashes need to be generated AFTER the substitution for it to be displayed correctly.