Problem with a Pettern Matching Check

Hello hopefully correct List,

I was trying to do something that is not working as it supposed to.
First I created a table:

create table t (
col CHAR (3) CONSTRAINT numonly_col CHECK ( col ~ '^\\d+$' )
);

This check avoids non-numbers like '1a1' and allows '123'. For some
reason, I'm unable to find out why, it also avoids things like '1' and
'12'. Could someone please give me hint? :)

I was trying this one on PostgreSQL 8.0.3

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Regards
Sebastian Siewior