multi-line regex

[Michael Mossey-2]

I have some very simple regex-matching needs, and Text.Regex.Posix will
work fine, EXCEPT I need to match multi-line patterns, and/or find all
occurrences of text that may occur several times on different lines. So I
need to turn on some kind of flag. Can someone show me how to do that? I
have worked the examples in RWH so I basically know how to run the thing.
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[Don Stewart-2]

mpm:
> I have some very simple regex-matching needs, and Text.Regex.Posix will  
> work fine, EXCEPT I need to match multi-line patterns, and/or find all  
> occurrences of text that may occur several times on different lines. So I
> need to turn on some kind of flag. Can someone show me how to do that? I  
> have worked the examples in RWH so I basically know how to run the thing.

Is that something that requires the PCRE bindings?
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[kenny lu]

Hi Michael,

Could you give an example of what patterns you want to write?

Regards,
Kenny

On Wed, Nov 4, 2009 at 1:35 PM, Michael Mossey <mpm@...> wrote:

I have some very simple regex-matching needs, and Text.Regex.Posix will work fine, EXCEPT I need to match multi-line patterns, and/or find all occurrences of text that may occur several times on different lines. So I need to turn on some kind of flag. Can someone show me how to do that? I have worked the examples in RWH so I basically know how to run the thing.
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[Michael Mossey-2]

kenny lu wrote:
> Hi Michael,
>
> Could you give an example of what patterns you want to write?
>
> Regards,
> Kenny
>

Something like

text = "11\n abcd \n22"
answer = text =~ "11.*22" :: <various possibilities>

and have it find the entire string. The default behavior is to stop
matching when it encounters a newline. There is mention in the
Text.Regex.Posix docs of a flag to control this behavior, but it is not
easy to figure out from the docs how to provide flags. The left-hand side
of the =~ is a very complex type.




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[kenny lu]

Michael,

Here is how I do it.


> module Main where

> import Text.Regex.Posix.ByteString
> import Data.Maybe
> import qualified Data.ByteString.Char8 as S

> text = S.pack "11\n abcd \n22"
> p = S.pack "11\n(.*)\n22"


> main :: IO ()
> main =
>  do  { (Right pat) <- compile compExtended execBlank p
>      ; res <- regexec pat text
>      ; case res of
>          { (Right (Just (_,_,_,m))) -> putStrLn (show m)        
>          ; _                        -> putStrLn "not matched."
>          }
>      }

You may swap out ByteString with String,
PCRE should be similar, too.

Regards,
Kenny

On Wed, Nov 4, 2009 at 2:04 PM, Michael Mossey <mpm@...> wrote:

kenny lu wrote:

Hi Michael,

Could you give an example of what patterns you want to write?

Regards,
Kenny

Something like

text = "11\n abcd \n22"
answer = text =~ "11.*22" :: <various possibilities>

and have it find the entire string. The default behavior is to stop matching when it encounters a newline. There is mention in the Text.Regex.Posix docs of a flag to control this behavior, but it is not easy to figure out from the docs how to provide flags. The left-hand side of the =~ is a very complex type.

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[David Leimbach]

Multi-line regular expressions are indeed powerful.  Rob Pike has a good paper on it available at:

http://doc.cat-v.org/bell_labs/structural_regexps/se.pdf

Explains how line-based regular expressions are limiting etc.

The Sam and Acme editors supported these.

Python does too now.

http://code.google.com/p/sregex/

On Wed, Nov 4, 2009 at 6:17 AM, kenny lu <haskellmail@...> wrote:

Michael,

Here is how I do it.


> module Main where

> import Text.Regex.Posix.ByteString
> import Data.Maybe
> import qualified Data.ByteString.Char8 as S

> text = S.pack "11\n abcd \n22"
> p = S.pack "11\n(.*)\n22"


> main :: IO ()
> main =
>  do  { (Right pat) <- compile compExtended execBlank p
>      ; res <- regexec pat text
>      ; case res of
>          { (Right (Just (_,_,_,m))) -> putStrLn (show m)        
>          ; _                        -> putStrLn "not matched."
>          }
>      }

You may swap out ByteString with String,
PCRE should be similar, too.

Regards,
Kenny

On Wed, Nov 4, 2009 at 2:04 PM, Michael Mossey <mpm@...> wrote:

kenny lu wrote:

Hi Michael,

Could you give an example of what patterns you want to write?

Regards,
Kenny

Something like

text = "11\n abcd \n22"
answer = text =~ "11.*22" :: <various possibilities>

and have it find the entire string. The default behavior is to stop matching when it encounters a newline. There is mention in the Text.Regex.Posix docs of a flag to control this behavior, but it is not easy to figure out from the docs how to provide flags. The left-hand side of the =~ is a very complex type.

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