about permissions

hi!
First short explanation:
I create application in php. In scripts I need sometimes check if user has
permissions to for example update values in some table

So question:
How should looks my queryi like?

I mean something like
select pg_class.relacl where relname='cust' and
pg_class.relacl[2]='my_user=arwR'; (this query doesn't work)

and another difficult problem:
I don't know what place in relacl array is occupied by permissions for my
user and of course can't check for string 'myuser=arwR' cause permissions
could be 'arw', 'ar', 'r'.
Naturally I can solve this by taking whole array and processing data in
php, but
I could be really fine to solve this inside postgres
TIA
Rem

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Remigiusz Sokolowski e-mail: rems(at)gdansk(dot)sprint(dot)pl * *
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