String interpretation

ruby-talk
1

The eval technique works for now--thanks! Is there also a way I can
reverse the conversion, i.e., getting a string with standard (not
RegExp) tokens from a string variable that has the actual characters,
themselves?

Jamal

···

-----Original Message-----
From: ara.t.howard@noaa.gov [mailto:ara.t.howard@noaa.gov]
Sent: Tuesday, April 25, 2006 2:28 PM
To: ruby-talk ML
Subject: Re: String interpretation

On Wed, 26 Apr 2006, Jamal Mazrui 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
--
be kind whenever possible... it is always possible.
- h.h. the 14th dali lama

2

with each and every feature creep you'll be wanting something like this:

   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
     def uninterpolate!
       INTERPOLATE.invert.each do |k,v|
         gsub! Regexp::new(Regexp::escape(k)), v
       end
     end
   end

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

   s.uninterpolate!
   p s
   puts s

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

cheers.

-a

···

On Wed, 26 Apr 2006, Jamal Mazrui wrote:

The eval technique works for now--thanks! Is there also a way I can
reverse the conversion, i.e., getting a string with standard (not
RegExp) tokens from a string variable that has the actual characters,
themselves?

--
be kind whenever possible... it is always possible.
- h.h. the 14th dali lama