st: problem with regexm leading to "regexp: unterminated ()" error for all observations

[Jamie Fagg <j.fagg@ich.ucl.ac.uk>]

Dear Stata users,

I've a problem with the function -regexm-. I get the following message:

regexp: unterminated ()

Frederico Belotti raised this in 2009 
(http://www.stata.com/statalist/archive/2009-04/msg00573.html) and 
Martin Weiss suggested contacting
Tech support but as far as I can see there is no other comment referring 
to the error.
(http://www.stata.com/statalist/archive/2009-04/msg00575.html).

My aim: to find out which of a list of 22,907 postcodes conform to the 
UK standard syntax.

I've never used regular expressions before, and I started trying to 
build the regular expression myself yesterday and ran a few options
with some (limited) success before a colleague pointed me to a 
pre-written regular expression on Wikipedia 
(http://en.wikipedia.org/wiki/Postcodes_in_the_United_Kingdom).
As this seems highly complex, has been done, and I really only want to 
do this once, it would be very helpful to be able to simply use it 
within Stata.

I have run the regular expression through a javascript regular 
expression checker here  (http://regexpal.com/) and it seemed to work 
correctly, picking out the valid (E1 4NS, SW8 2XR)
versions of the postcodes in the example below.

This is an example of the code I used plus sample data if users want to 
see if they can reproduce the error.

I would very much appreciate any feedback about this,

Best wishes,

Jamie

******start of example*********

input str15 postcode
E1 4NS
EI 4NS
SW8 2XR
SW8 ZXR
end

#delimit ;

//regular expression to define whether postcode is syntactically correct

ge postcodevalid = 1 if regexm(postcode,"(GIR 0AA)|(((A[BL]|B[ABDHLNRSTX]
?|C[ABFHMORTVW]|D[ADEGHLNTY]|E[HNX]?|F[KY]|G[LUY]?|H[ADGPRSUX]
|I[GMPV]|JE|K[ATWY]|L[ADELNSU]?|M[EKL]?|N[EGNPRW]?|O[LX]|P[AEHLOR]
|R[GHM]|S[AEGKLMNOPRSTY]?|T[ADFNQRSW]|UB|W[ADFNRSV]|YO|ZE)[1-9]?[0-9]
|((E|N|NW|SE|SW|W)1|EC[1-4]|WC[12])[A-HJKMNPR-Y]|(SW|W)([2-9]|[1-9]
[0-9])|EC[1-9][0-9]) [0-9][ABD-HJLNP-UW-Z]{2})")==1;

*****end of example*******

******My Stata specs********

Stata/SE 11.1 for Windows (32-bit)

Stata executable
folder: C:\Program Files\Stata11\
name of file: StataSE.exe
currently installed: 04 Nov 2010

Ado-file updates
folder: C:\Program Files\Stata11\ado\updates\
names of files: (various)
currently installed: 04 Jan 2011

Utilities updates
folder: C:\Program Files\Stata11\utilities
names of files: (various)
currently installed: 01 Sep 2010


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