From: Robert Klemme <shortcutter@...>
Date: 2008-06-16T18:10:43+09:00
Subject: Re: how to stop gsub from returning nil

2008/6/16 Tom Cloyd <tomcloyd@comcast.net>:
> I'm trying to use gsub to do a number of transformations in an array of
> strings. I find that when a particular transformation does NOT happen,
> because the searched-for substring is not there, gsub returns nil. This
> effectively ruins my output. I don't want nothing. I want the string that's
> being processed, returned with or without any transformations. Is there any
> alternative to testing for a return of nil before calling gsub, so as to
> avoid the wiping out of my string? I've looked for something to use other
> than String::gsub, and have not found anything.

You first need to decide whether you want to do all your
transformations in place (i.e. on the original strings in the Array)
or whether you need a copy of all strings - with or without changes.

> Code:
>
> filein = open( "{whatever}" )
> fi = filein.readlines
> delta = [ ["</p>", ''], ["</h1>", ''] ]
> results = fi.collect do |x|
>  delta.each do |y|
>   debugger             x.gsub!(y[0], y[1])
>  end
> end

It's not clear what you intend to do with results, but I assume for
the moment that you need copies.  In that case you probably should not
use String#gsub! but String#gsub (i.e. the version which leaves the
original untouched).

Few other remarks:

- You do not use the block form of file opening and thus you leave the
file descriptor open which is bad.

- You can read a complete file as Array via File.readlines("whatever")

- You can read a complete file as String via File.read("whatever")

- a Hash seems more appropriate for delta because it nicely expresses
the key value relationship between search criteria and replacement
string and also prevents accidental duplicates.  Downside is that you
loose order if that is important for you.

- Reading the file as single String might be more efficient because in
that case you only need one gsub per replacement expression

So, here's probably what I'd do

delta = { %r{</(?:p|h1)>}i => '' }

c = File.read "whatever.html"
delta.each do |rx, repl|
  c.gsub! rx, repl
end

puts c

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end