# String interpretation

**URL:** <https://www.ruby-forum.com/t/string-interpretation/58774>\
**Category:** Ruby\
**Created:** [April 25, 2006, 8:12pm UTC](https://www.ruby-forum.com/t/string-interpretation/58774 "2006-04-25T20:12:55Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![jamal86](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ebca7d/32.png) [@jamal86](https://www.ruby-forum.com/u/jamal86)\
**Post date:** [April 25, 2006, 8:12pm UTC](https://www.ruby-forum.com/t/string-interpretation/58774/1 "2006-04-25T20:12:55Z")

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First, I’m curious why a string delimited with apostrophe characters is  
not interpreted completely literally. Why does the language make an  
exception for the backslash character so that it needs to be doubled  
there as well?

Second, how do I ensure that tokens are translated in a string variable?  
I am developing a program with a search feature. I want the user to be  
able to indicate carriage return, line feed, tab, and form feed  
characters using the standard tokens of \r, \n, \t, and \f. I do not  
want them to have to specify a true regular expression, however, since  
other characters such as a period would then need to be escaped and I  
want to minimize user knowledge requirements.

If I save the user’s find string to a variable (using WxRuby), and then  
search for it using the index method, tokens such as \n are interpreted  
literally. I thought that maybe

input = “#{input}”  
would translate the characters, but this does not work, and I have not  
yet found a way.

Jamal

---

<div class="post-metadata">

**Author:** ![jamal86](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ebca7d/32.png) [@jamal86](https://www.ruby-forum.com/u/jamal86)\
**Post date:** [April 25, 2006, 8:16pm UTC](https://www.ruby-forum.com/t/string-interpretation/58774/2 "2006-04-25T20:16:02Z")

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Hi –

On Wed, 26 Apr 2006, Jamal M. wrote:

> First, I’m curious why a string delimited with apostrophe characters is  
> not interpreted completely literally. Why does the language make an  
> exception for the backslash character so that it needs to be doubled  
> there as well?

Because you need the backslash to do:

‘'’

so then you need a way to indicate the backslash itself 🙂

David

–  
David A. Black (removed\_email\_address@domain.invalid)  
Ruby Power and Light, LLC ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com))

“Ruby for Rails” PDF now on sale! [Ruby for Rails](http://www.manning.com/black)  
Paper version coming in early May!

---

<div class="post-metadata">

**Author:** ![jamal86](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/ebca7d/32.png) [@jamal86](https://www.ruby-forum.com/u/jamal86)\
**Post date:** [April 25, 2006, 8:28pm UTC](https://www.ruby-forum.com/t/string-interpretation/58774/3 "2006-04-25T20:28:26Z")

</div>

On Wed, 26 Apr 2006, Jamal M. wrote:

> Second, how do I ensure that tokens are translated in a string variable?  
> I am developing a program with a search feature. I want the user to be  
> able to indicate carriage return, line feed, tab, and form feed  
> characters using the standard tokens of \r, \n, \t, and \f. I do not  
> want them to have to specify a true regular expression, however, since  
> other characters such as a period would then need to be escaped and I  
> want to minimize user knowledge requirements.

irb(main):007:0\> s = ‘foo\tbar\n’  
=\> “foo\tbar\n”

irb(main):008:0\> s = eval “%Q(#{ s })”  
=\> “foo\tbar\n”

irb(main):009:0\> puts s  
foo bar  
=\> nil

but i would advise against this. instead, just make a little parser  
class:

```
 harp:~ > cat a.rb
 class SearchExpression < ::String
   INTERPOLATE = {
     '\n' => "\n",
     '\t' => "\t",
     '\r' => "\r",
     '\f' => "\f",
   }
   def initialize *a, &b
     super and interpolate!
   end
   def interpolate!
     INTERPOLATE.each do |k,v|
       gsub! Regexp::new(Regexp::escape(k)), v
     end
   end
 end

 s = SearchExpression::new 'foo\tbar\n'

 p s
 puts s

 harp:~ > ruby a.rb
 "foo\tbar\n"
 foo bar

```

easy cheasy.

-a