Uses a list of regular expressions and replacement strings
to make changes in text files.

Put in file "edit-all.rb" and run with
ruby edit-all.rb *.txt

Now accepts the target and the replacement from the command line or from the keyboard.

##
##  Make substitutions in a slew of files.
##  Backups having the extension ".bak" are made.
##  To make it descend into all subdirectories:
##    ruby edit-all.rb **/*.txt
##
##  You may include the target & replacement on the
##  command line by using the -x switch:
##    ruby edit-all.rb -x 'original' 'replacement' *.txt

# Only files below the current level?
only_deep = false

pairs = [
#   /Original text\./,  "Edited in place.",
#   /(\w+) text\./,  '\1 nonsense.'
]

if '-x' == ARGV.first
  ARGV.shift
  pairs = [ Regexp.new( ARGV.shift ), ARGV.shift ]
end

if pairs.size == 0
  puts "\nIn the replacement text, use \\1 for the first"
  puts "capture, \\2 for the second, etc.\n\n"
  loop {
    print "regular expression: "
    s = STDIN.gets.chomp
    break if s == ""
    pairs << Regexp.new( s )
    print "replacement: "
    pairs << STDIN.gets.chomp
  }
end

raise "\npairs must contain even number of items."  if
  1 == pairs.size % 2

ARGV.reject! { |f| File.directory?(f) }
ARGV.reject! { |f| f !~ /\// }   if only_deep

if ARGV.empty?
  puts "I have no filenames."
  exit
end

# Turn on in-place editing.  If you're certain that
# nothing can go wrong, you may want to turn off
# creation of backups by changing ".bak" to "" (won't
# work under windoze).
$-i = ".bak"

ARGF.each{ |line|
  (0 ... pairs.size).step(2) { |i|
      line.gsub!( pairs[i], pairs[i+1]  )
  }
  puts line
}