From: Warren Brown <warrenb@...>
Date: 2007-08-02T07:08:48+09:00
Subject: Re: oddity with RegExp

Russell,

> I'm clearly missing something!  I have a log analysis
> application that is written in Ruby and which uses
> REs to decide how to process log records.
> 
> I entered a pattern into one of my rules and it always
> failed to match so I fired up irb and set about
> reducing the pattern to something minimal:
> 
> [rful011@pateke selms-svn]$ irb
> irb(main):001:0> a = 'NT AUTHORITY\SYSTEM'
> => "NT AUTHORITY\\SYSTEM"
> irb(main):004:0> a =~ /AUTHORITY/
> => 3
> irb(main):005:0> a =~ /NT AUTHORITY/
> => 0
> irb(main):006:0> a =~ / AUTHORITY/
> => 2
> irb(main):007:0> a =~ /^NT /
> => 0
> irb(main):008:0> a =~ /NT /
> => 0
> irb(main):009:0> a =~ /NT/
> => 0
> irb(main):010:0> a =~ /N/
> => 0
> irb(main):011:0> a =~ /T/
> => 1
> 
> Is the '\' in the string upsetting things?

    No, you are just misinterpreting the results.

irb(main):001:0> a = 'NT AUTHORITY\SYSTEM'
=> "NT AUTHORITY\\SYSTEM"
irb(main):002:0> a =~ /N/
=> 0
irb(main):003:0> a =~ /X/
=> nil

    Zero is a valid string index, nil is not.

    - Warren Brown