Regex bug?

[originally sent to vw-dev, my bad]

Shouldn't both of these answer true?

'^ab' asRegex matches: '   ab'
'\<ab' asRegex matches: '   ab'

From the #c:syntax:

\<   an empty string at the beginning of a word
^    matching an empty string at the beginning of a line

Thanks!

-Boris

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Hello Boris,

Except if Regex for VW has specific behavior but the first regex
expression could not be true, it means the first character of a line is
an 'a' followed by a 'b', and in your example, you have some white
spaces before a and b

For the second one, no idea

Regards,
Marc-Philippe

Boris Popov a écrit :

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Boris Popov wrote:
Both expressions above properly return false, because:
        1) Sending #matches: to the regex means match the whole input and not just
           a portion of it.
        2) '^' stands for begining of line - it matches specific position (an *empty*
           string) therefore leading white spaces violate the pattern.
        3) '\<' (resp. '\>') matches *empty* string at the begining (resp. end) of
           a word therefore leading white spaces violate the pattern again.

Note also that *empty* string stands for ''.

The intended usage of '\<' and '\>' is like this:
        '.*\<ab\>.*' asRegex matches: 'ab' "true"
        '.*\<ab\>.*' asRegex matches: ' ab' "true"
        '.*\<ab\>.*' asRegex matches: ' ab ' "true"
        '.*\<ab\>.*' asRegex matches: 'ab ' "true"
BUT
        '.*\<ab\>.*' asRegex matches: 'aab' "false"
        '.*\<ab\>.*' asRegex matches: 'aabb' "false"
        '.*\<ab\>.*' asRegex matches: 'abb' "false"
So the pattern above matches all strings that contain *word* 'ab'.

Hope this helps,

Ladislav Lenart

Thanks, this makes quite a bit more sense now and the examples helped quite
a bit.

Cheers!

-Boris

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+1.604.689.0322
DeepCove Labs Ltd.
4th floor 595 Howe Street
Vancouver, Canada V6C 2T5

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This email is intended only for the persons named in the message
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-----Original Message-----
From: Ladislav Lenart [mailto:[hidden email]]
Sent: Tuesday, May 16, 2006 12:45 AM
To: [hidden email]
Subject: Re: Regex bug?

Boris Popov wrote: Both expressions above properly return false, because:
        1) Sending #matches: to the regex means match the whole input and
not just
           a portion of it.
        2) '^' stands for begining of line - it matches specific position
(an *empty*
           string) therefore leading white spaces violate the pattern.
        3) '\<' (resp. '\>') matches *empty* string at the begining (resp.
end) of
           a word therefore leading white spaces violate the pattern again.

Note also that *empty* string stands for ''.

The intended usage of '\<' and '\>' is like this:
        '.*\<ab\>.*' asRegex matches: 'ab' "true"
        '.*\<ab\>.*' asRegex matches: ' ab' "true"
        '.*\<ab\>.*' asRegex matches: ' ab ' "true"
        '.*\<ab\>.*' asRegex matches: 'ab ' "true"
BUT
        '.*\<ab\>.*' asRegex matches: 'aab' "false"
        '.*\<ab\>.*' asRegex matches: 'aabb' "false"
        '.*\<ab\>.*' asRegex matches: 'abb' "false"
So the pattern above matches all strings that contain *word* 'ab'.

Hope this helps,

Ladislav Lenart