How to convert a string with special characters escaped to the actual special chars

Question

How to convert a string with special characters escaped to the actual special chars?

For example, if I have this:

s = "hello\\nworld"

The output of puts is naturally this:

> puts s
hello\nworld

But how do I transform it into this?

hello
world

In other words, is there any function to unescape backslashed characters?

Duplicate of [How do I unescape c-style escape sequences from ruby?](http://stackoverflow.com/q/4265928/3425536) — Emil Laine, Mar 23 '17 at 20:49
Best answer I found so far : http://stackoverflow.com/a/22090177/6419007 — Eric Duminil, Mar 23 '17 at 21:01

score 2 · Answer 1 · answered Mar 23 '17 at 20:23

2

Your best bet is to do some string replacements.

s = "hello\\nworld"
puts s.gsub("\\n", "\n")
# >> hello
# >> world

The downside of this approach is that you have to explicitly list/process all special chars you need to unescape.

answered Mar 23 '17 at 20:23

Sergio Tulentsev

1

I guess that table substitutions in double quoted will be helpful - [table](https://i.stack.imgur.com/83EBc.png) – Dmitry Cat Mar 23 '17 at 20:26
The approach is something like that, but I really want to avoid that. That makes an ugly code... – rigon Mar 23 '17 at 20:29
@rigon: yeah well, you're free to prefer elegant `eval`. But I wouldn't recommend that. Out of curiousity, what exactly do you think is "ugly" about this piece of code? – Sergio Tulentsev Mar 23 '17 at 20:31
Because of this: https://github.com/ruby/ruby/blob/trunk/doc/syntax/literals.rdoc#strings To cover all the possibilities is pretty complex. And I agree with you, the `eval` approach is a way worse. Ruby doesn't something like this `s.unescape_special_chars`? – rigon Mar 23 '17 at 20:38
1

@rigon This really *doesn't* make for ugly code. You should be putting your logic in `escape` and `unescape` methods, or using such already written methods as provide by other libraries – user229044 Mar 23 '17 at 20:42
@meagar Which libraries does that? – rigon Mar 23 '17 at 20:43
@rigon: as meagar says. Also instead of chaining gsubs (`gsub(...).gsub(...).gsub(...)`), you can put all substitutions in a hash/table and do a clever `reduce` on it. – Sergio Tulentsev Mar 23 '17 at 20:44
2

@rigon See https://stackoverflow.com/questions/9683985/unescaping-special-character-sequences-in-ruby-strings – user229044 Mar 23 '17 at 20:44

score 0 · Answer 2 · edited Feb 04 '20 at 01:13

0

You interpolate \ by \\ , use one backslash instead of two:

s = "hello\nworld"
puts s 
#=> hello
    world

edited Feb 04 '20 at 01:13

the Tin Man

answered Mar 23 '17 at 20:02

Dmitry Cat

2

Maybe I wasn't clear in the question, but I'm receiving an escaped string with backslashes and I want to unescape it, returning to the original string. – rigon Mar 23 '17 at 20:05
You can use gsub, s.gsub('\\','\') – Dmitry Cat Mar 23 '17 at 20:10
1

@DmitryCat `s.gsub('\\','\')` doesn't work. `'\'` is not a valid string, `\ ` escapes the `'`. – Emil Laine Mar 23 '17 at 20:16

Emil Laine · Answer 3 · 2017-03-23T20:35:12.493

-3

If your string is from a trusted source, you can use eval:

s = "hello\\nworld"    
eval("\"#{s}\"") # => "hello\nworld"

Note that this allows arbitrary code execution:

s = "\"; loop { }; \""
eval("\"#{s}\"") # => infinite loop

Also this doesn't work for input like s = "\"".

edited Mar 23 '17 at 20:35

answered Mar 23 '17 at 20:07

Emil Laine

what will happen if s = "User.delete_all" for example or "while true puts 'kek'"? – Dmitry Cat Mar 23 '17 at 20:09
@DmitryCat It returns the string as expected? (Note the quotes.) – Emil Laine Mar 23 '17 at 20:11
1

yes, but s = "\"" returns error – Dmitry Cat Mar 23 '17 at 20:14
1

This is really bad, and the fact that you think wrapping it in quotes is somehow effective just demonstrates how problematic `eval` actually is. You have done absolutely nothing to prevent arbitrary code execution. This does **not** "work against malicious input". – user229044 Mar 23 '17 at 20:32
4

@tuple_cat `'#{User.destory_all}'`, or `'"; User.destroy_all; "'` or any number of a million others. – user229044 Mar 23 '17 at 20:34

3 Answers3