From: Nate Wiger <nwiger@...>
Date: 2006-10-21T03:40:16+09:00
Subject: Easy way to check is sub!() succeeds?

Hi all, I'm trying to port some Perl code to Ruby as part of learning 
the language. This code is part of a script called "untar", which is a 
simple suffix-based wrapper around unzip/cpio/gunzip/tar/etc.

It starts with suffix to command maps:

   zip = {
     'gz'  => 'gunzip -c',
     'Z'   => 'uncompress -c',
     'zip' => 'unzip',
     'bz2' => 'bunzip2 -c'
   }

I then want to loop over all files specified, and check if the suffix 
matches. If so, I want to strip it and set the proper command. My first 
attempt was this:

   ARGV.each do |file|
     zip.each do |suf, cmd|
       if file.sub!(%r{\.#{suf}$}, '')
         untar = cmd
         break
       end
     end
     # ... more code
   end

But sub! always returns nil, even when it succeeds (in Perl, it will 
return the number of substitutions made, enabling "next if s/\.$suf$//")

So now I have this:

   ARGV.each do |file|
     zip.each do |suf, cmd|
       if (new = file.sub(%r{\.#{suf}$}, '')) != file
          unzip = cmd
          file  = new
          break
       end
     end
     # ... more code
   end

Which works, but is not so pretty. Any ideas?

-Nate

P.S. This script allows multiple suffices, aka .tar.bz2, .tar.gz, etc, 
hence why it needs to loop repeatedly and strip each one (much code is 
not shown above)