From: Robert Klemme <shortcutter@...>
Date: 2007-08-17T22:47:53+09:00
Subject: Re: file grep

2007/8/16, Felix Windt <fwmailinglists@gmail.com>:
> > -----Original Message-----
> > From: list-bounce@example.com
> > [mailto:list-bounce@example.com] On Behalf Of Abhijeet Dharmapurikar
> > Sent: Thursday, August 16, 2007 12:51 PM
> > To: ruby-talk ML
> > Subject: file grep
> >
> > I have a file that has a list of filenames- filenames.txt I
> > have another file that has list of all the files in the
> > system with their complete filepaths - allfilespath.txt
> >
> > I want to print the fullpaths of all the files listed in
> > filenames.txt In shell scripting I would have done somethign like this
> >
> > for name in filenames.txt
> > do
> >   grep $name allfilespath.txt
> >   if [ $? == 1 ]
> >   then
> >     echo $output_from_grep
> >   fi
> > done
> >
> >
> > How do I do this in ruby  ? If possible (again if possible)
> > explain what the code does. If not I will google and update
> > what each line does.
>
> Disclaimer: Reading the complete files in to arrays like this may cost a
> bunch of memory depending on file size

Here's another solution that avoids reading the large file into mem
but it does not write out names ordered:

require 'set'
names = Set.new(File.readlines("filenames.txt").each {|s| s.chomp!})

File.open("allfilespath.txt") do |io|
  io.each do |line|
    line.chomp!
    puts line if names.includes? File.basename(line)
  end
end

Kind regards

robert