POSIX RE starting with a (

Nick Barr wrote:

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!

Sorry should of said I am running PG 7.4.3.

Nick

Nick Barr <nicky@chuckie.co.uk> writes:

intranet=# select track_name from ms_track where track_name ~ '^\(';
ERROR: invalid regular expression: parentheses () not balanced

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

On Wed, 2004-08-11 at 14:39, Nick Barr wrote:

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?

You need to escape the backslash:

select track_name from ms_track where track_name ~ '^\\
(';
--
Oliver Elphick olly@lfix.co.uk
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

Tom Lane wrote:

Nick Barr <nicky@chuckie.co.uk> writes:

intranet=# select track_name from ms_track where track_name ~ '^\(';
ERROR: invalid regular expression: parentheses () not balanced

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

Doh,

Thanks guys.

Nick

On Wed, Aug 11, 2004 at 03:28:17PM +0100, Nick Barr wrote:

======================================================================
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?

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

http://www.postgresql.org/docs/7.4/static/functions-matching.html#POSIX-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/