From: Justin Collins <justincollins@...>
Date: 2011-01-16T12:20:03+09:00
Subject: Re: Regexp - start and end of line or string

On 01/15/2011 06:43 PM, Colin Bartlett wrote:
> How often do people use \A and \z (match start and end of a string)
> instead of ^ and $ (match start and end of a line within a string)?
>
> This question is prompted by:
>
> (1) part of a post in the "What are your ruby rough cuts ?" thread:
>    * Regexp ^ and $ work match more than just start and end of string.
>    For example, /^abc$/ does not match only "abc" but also "rm -rf /*\nabc"
>
> Comment: using \A and \z seems to avoid the unwanted(?) matches.
> Am I missing something?
>    

Most of the time I am going through data a line at a time, so this is 
not a concern.

However, it seems to me that many people are not aware of this 
distinction, thus we have things like this: 
http://guides.rubyonrails.org/security.html#regular-expressions

> (2) a Regexp used in the Find module
>      if File::ALT_SEPARATOR and file =~ /^(?:[\/\\]|[A-Za-z]:[\/\\]?)$/ then
>    which matches "start of a line" + X + "end of a line",
>    where X is one of   /   \\   C:   C:/   C:\\
>
> Comment: using ^ and $ in Find will match in the (admittedly rather
> unlikely) situation of a file path string containing "\n/\n", and I'm
> wondering why ^ and $ are used in this Find module regexp instead of
> using \A and \z.
>    

I suppose this is a bug.

-Justin