POSIX RE starting with a (

Nick Barr wrote:
[color=blue]
> Hi,
>
> Just noticed something funny with the POSIX Regular expressions and
> wondered if it is a bug, or whether I am doing something wrong. I am
> using the POSIX RE in a function that is used in several places so would
> have to put some nasty if statement in there for this side case if there
> is not work around.
>
> ================================================== ====================
> intranet=# select track_id, track_name from ms_track where track_name
> like '(%';
> track_id | track_name
> ----------+---------------------------------
> 1294 | (I Can''t Get No) Satisfaction
> 1340 | (Hidden Track)
> 1503 | (Nice Dream)
> 1942 | (I) Get Lost
> (4 rows)
>
> intranet=# select track_name from ms_track where track_name ~ '^\(';
> ERROR: invalid regular expression: parentheses () not balanced
> intranet=# select track_name from ms_track where track_name ~ '^(';
> ERROR: invalid regular expression: parentheses () not balanced
> intranet=# select track_name from ms_track where track_name ~ '^\(';
> ERROR: invalid regular expression: parentheses () not balanced
> ================================================== ====================
>
> Now I have tried a similar query using the PHP POSIX Regular Expressions
> and it accepts the sequence '^\(' and matches correctly. Is this a
> "feature" of PG that cannot be worked around easily?
>
> Any thoughts?
>
> Thanks
>
> Nick
>
> P.S. Thanks a lot guys for all the hard work on 8.0, looks good to me.
> Lots of really useful features, PITR, Win32, Nested transactions. Good
> work guys![/color]

Sorry should of said I am running PG 7.4.3.


Nick


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Nick Barr <nicky@chuckie.co.uk> writes:[color=blue]
> intranet=# select track_name from ms_track where track_name ~ '^\(';
> ERROR: invalid regular expression: parentheses () not balanced[/color]

You've forgotten that the string-literal parser will eat one level of
backslashing. You need

intranet=# select track_name from ms_track where track_name ~ '^\\(';

to get that backslash into the regex parser.

regards, tom lane

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On Wed, 2004-08-11 at 14:39, Nick Barr wrote:[color=blue]
> Hi,
>
> Just noticed something funny with the POSIX Regular expressions and
> wondered if it is a bug, or whether I am doing something wrong. I am
> using the POSIX RE in a function that is used in several places so would
> have to put some nasty if statement in there for this side case if there
> is not work around.
>
> ================================================== ====================
> intranet=# select track_id, track_name from ms_track where track_name
> like '(%';
> track_id | track_name
> ----------+---------------------------------
> 1294 | (I Can''t Get No) Satisfaction
> 1340 | (Hidden Track)
> 1503 | (Nice Dream)
> 1942 | (I) Get Lost
> (4 rows)
>
> intranet=# select track_name from ms_track where track_name ~ '^\(';
> ERROR: invalid regular expression: parentheses () not balanced
> intranet=# select track_name from ms_track where track_name ~ '^(';
> ERROR: invalid regular expression: parentheses () not balanced
> intranet=# select track_name from ms_track where track_name ~ '^\(';
> ERROR: invalid regular expression: parentheses () not balanced
> ================================================== ====================
>
> Now I have tried a similar query using the PHP POSIX Regular Expressions
> and it accepts the sequence '^\(' and matches correctly. Is this a
> "feature" of PG that cannot be worked around easily?[/color]

You need to escape the backslash:

select track_name from ms_track where track_name ~ '^\\
(';
--
Oliver Elphick Join Bytes!
Isle of Wight http://www.lfix.co.uk/oliver
GPG: 1024D/A54310EA 92C8 39E7 280E 3631 3F0E 1EC0 5664 7A2F A543 10EA
========================================
"Be still before the LORD and wait patiently for him;
do not fret when men succeed in their ways, when they
carry out their wicked schemes."
Psalms 37:7


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Tom Lane wrote:[color=blue]
> Nick Barr <nicky@chuckie.co.uk> writes:
>[color=green]
>>intranet=# select track_name from ms_track where track_name ~ '^\(';
>>ERROR: invalid regular expression: parentheses () not balanced[/color]
>
>
> You've forgotten that the string-literal parser will eat one level of
> backslashing. You need
>
> intranet=# select track_name from ms_track where track_name ~ '^\\(';
>
> to get that backslash into the regex parser.
>
> regards, tom lane
>
>
>[/color]

Doh,

Thanks guys.


Nick


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On Wed, Aug 11, 2004 at 03:28:17PM +0100, Nick Barr wrote:
[color=blue]
>================================================== ====================
>intranet=# select track_id, track_name from ms_track where track_name
>like '(%';
> track_id | track_name
>----------+---------------------------------
> 1294 | (I Can''t Get No) Satisfaction
> 1340 | (Hidden Track)
> 1503 | (Nice Dream)
> 1942 | (I) Get Lost
>(4 rows)
>
>intranet=# select track_name from ms_track where track_name ~ '^\(';
>ERROR: invalid regular expression: parentheses () not balanced
>intranet=# select track_name from ms_track where track_name ~ '^(';
>ERROR: invalid regular expression: parentheses () not balanced
>intranet=# select track_name from ms_track where track_name ~ '^\(';
>ERROR: invalid regular expression: parentheses () not balanced
>================================================== ====================
>
>Now I have tried a similar query using the PHP POSIX Regular Expressions
>and it accepts the sequence '^\(' and matches correctly. Is this a
>"feature" of PG that cannot be worked around easily?[/color]

See the "Regular Expression Details" section of the PostgreSQL manual:

http://www.postgresql.org/docs/7.4/...-SYNTAX-DETAILS

The Note under Table 9-12 says, "Remember that the backslash (\)
already has a special meaning in PostgreSQL string literals. To
write a pattern constant that contains a backslash, you must write
two backslashes in the statement."

Try this:

SELECT track_name FROM ms_track WHERE track_name ~ '^\\(';

--
Michael Fuhr
http://www.fuhr.org/~mfuhr/

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