From: Keith Fahlgren <keith@...>
Date: 2005-07-29T01:18:26+09:00
Subject: Sed -> Ruby : .. and ...

Hi all,

What's the deal with all the different versions of 
http://pleac.sourceforge.net/pleac_ruby/patternmatching.html on the 
web? I've found that the most complete document and most helpful on 
this sort of Ruby regular expression tutelage. 

It seems like documentation on adopting sed to Ruby would be helpful. 
[I'll write something if I ever understand it.]

Surprise: I'm trying to adapt some sed scripts into Ruby programs. I'd 
like feedback on how to make them more idiomatic/Rubylicious and help 
on making 2nd one work.

Here's my essential program for a line of sed that seems to work 
correctly. I dunno if there's a better way to express it:

---------------------------------------------------

sed:
s/MATCH/GLOBAL REPLACEMENT/g

ruby:
#!/usr/bin/env ruby

files = ARGV

files.each do |arg|
  f = File.open(arg)
  puts "\nOpening file #{f}"
  working_file = f.read

  working_file.gsub!(/MATCH/,'GLOBAL REPLACEMENT')

  puts "\nDoing ACTION in #{arg}"
  f = File.new(arg, "w")
  puts "\nWriting #{f} now"
  f.print(working_file)
  f.close
end

---------------------------------------------------

Here's the one I have problems with (we had a working Perl equivalent 
but are trying to abandon Perl). 

sed:
/BEGIN RANGE/,/END RANGE/{
        s/MATCH/REPLACEMENT/g
}

ruby:
[same beginning]
  if working_file =~ /BEGIN RANGE/ .. working_file =~ /END RANGE/    
    # INCLUSIVE use ... if you want non inclusive
    working_file.sub!(/MATCH/,'REPLACEMENT')
  end
[same ending]
-----------------

The above works fine on the first occurence of MATCH but won't do any of 
the subsequent matches in the document. I subsitute 'gsub' but that 
will just effect all of the places in the document, ignoring my if 
statement. Suspecting a lack of understanding of the way the range 
works and find and old thread on the mailing list 
( http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/73674 ) 
but don't really follow it.

I've come up with the following as a tentative replacement but it's not 
setting 'aline' in 'working_file' after it substitues it.

[same beginning]
  working_file.each do |aline|    # Read each line, right?
    if aline =~ /BEGIN RANGE/ .. aline =~ /# end of CellContent/    
      aline.sub!(/Cell/,'CellHeading2')
    end
  end
[same ending]
-----------------

[Running up against my own ignorance now of the range thingie]
Here's my failing test:
#!/usr/bin/env ruby
files = ARGV
files.each do |arg|
  f = File.open(arg)
  puts "\nOpening file #{f}"
  working_file = f.read
  puts "Subsitutions occuring now"
  working_file.each do |aline|
    if aline =~ /BEGIN RANGE/ .. aline =~ /END RANGE/    
      aline.sub!(/MATCH/,'REPLACEMENT')
      puts "#{aline}"
    end
  end
  puts "\nOutput of working_file"
  puts "#{working_file}"
  puts "\nDoing ACTION in #{arg}"
  f = File.new(arg, "w")
  puts "\nWriting #{f} now"
  f.print(working_file)
  f.close
end

-----------------
Here's the test file:
a lonely line
BEGIN RANGE
  MATCH
END RANGE
another lonely line
BEGIN RANGE
  MATCH
  nothing here
  MATCH
END RANGE
don't change MATCH

-----------------
Here's the output:
> ,rtest2 ,test.txt

Opening file #<File:0xff3f0>
Subsitutions occuring now
BEGIN RANGE
  REPLACEMENT
END RANGE
BEGIN RANGE
  REPLACEMENT
  nothing here
  REPLACEMENT
END RANGE

Output of working_file
a lonely line
BEGIN RANGE
  MATCH
END RANGE
another lonely line
BEGIN RANGE
  MATCH
  nothing here
  MATCH
END RANGE
don't change MATCH



Doing ACTION in ,test.txt

Writing #<File:0xfeef8> now


Thanks for your help,
Keith