From: Paul Duncan <pabs@...>
Date: 2002-04-16T05:00:22+09:00
Subject: Re: need help on using Ruby to replace some SED expressions


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* kackson (kackson@yahoo.com) wrote:
> I tried sed. But it is getting really tough when I keep realizing I've
> things to expand and expand and expand into a huge chunk of regular
> expressions that now become completely unreadable and hard to
> maintain.
> So, as a beginner of Ruby, any advise on the question below is
> apprecaited.
>=20
> I need to:
> 1. read an input file
> 2. For everyline, if the FIRST word has a dot '.', replace it with $.
> Note, the first word may/maynot have been indented.
> 3. For the rest of the line, replace all occurance of '@' with '^'.
> 4. If there is something like '(2 + 3)' somewhere along the line,
> evaluate it and replace the entire expression i.e. (2 + 3) with the
> result, i.e. 5. Note, the brackets are gone. And it could be +, *, -,
> or divide. If it is even possible for mathmatical routines such as
> log/sin, etc. That would be even better.

This is almost what you need:
----
#!/usr/bin/ruby

lines =3D []
math_re =3D /\(([()+\-*\/\d\s]{3,})\)/
result =3D 0

input_file =3D ARGV.shift or die 'missing arguments'

File.open(input_file) { |f|
  f.each { |line|=20
    line.sub!(/\./, '$') if line =3D~ /^\s*([\w\.]+)/
    line.gsub! /\@/, '^'

    if matches =3D math_re.match(line)
      (1...matches.length).each { |i|
        begin
          eval "result =3D #{matches[i]}" # WARNING: possible security hole
          line.gsub! Regexp.new(Regexp.escape matches[i]), result.to_s
        rescue =3D>detail
          $STDERR.puts "Invalid math match: '#{matches[i]}'"
        end
      }
    end

    puts line
  }
}
----
Test file and results:

pabs@bobby:~/proj/blah> cat test.txt && echo '----' && ./blah.rb test.txt
  asdf.asdf # should replace the first .
asdfasdfasdf (5+3) # should change 5+3 to 8
asdf.asdfsadf.afdafk.asdf # should only change the first dot
  @@@@@@@@@@@@@@@@@ # should change at symbol to caret
----
  asdf$asdf # should replace the first .
asdfasdfasdf (8) # should change 8 to 8
asdf$asdfsadf.afdafk.asdf # should only change the first dot
^^^^^^^^^^^^^^^^^ # should change at symbol to caret
----

> I'm running short of time to experiment all the powerful set of ruby
> methods for now. I hope some ruby expert could help.

Hope this helps...

PS I'm sure the real ruby experts can come up with an even more elegant
solution :)

> Thank you!!!

--=20
Paul Duncan <pabs@pablotrin.org>        pabs in #gah (OPN IRC)
http://www.pablotron.org/               OpenPGP Key ID: 0x82C29562

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