From: 7stud -- <bbxx789_05ss@...>
Date: 2009-09-20T13:58:49+09:00
Subject: Re: Regexp question difference between ^ and \A

Hunt Jon wrote:
> Hi
> 
> I'm trying to find good use examples to show a difference
> between ^ and \A in Ruby regular expressions.
> 
> \A is for beginning of a string
> ^ beginning of a line or string
> 
> As a regular expression runs one line by line (if I'm correct),
> I think both are the same.
> 

What does "runs one line by line" mean?   A regular expression may 
examine the whole darn string--character by character.  For example:

str = "abc\n123"
results = str.scan(/./m)
p results

--output:--
["a", "b", "c", "\n", "1", "2", "3"]

Do you consider that "runs one line by line"?

\A matches just before the *FIRST* character of a string--and nowhere 
else:

str = "abc\n123"
results = str.scan(/\A.../)
p results

--output:--
["abc"]


^ matches just before the *first* character of a string,  *AND* just 
after any newline:

str = "abc\n123"
results = str.scan(/^.../)
p results

--output:--
["abc", "123"]

If your string doesn't have any newlines, guess what?

str = "abc123"
results = str.scan(/\A.../)
p results

--output:--
["abc"]


str = "abc123"
results = str.scan(/^.../)
p results

--output:--
["abc"]

... \A and ^ are equivalent.
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