problem with copy command

dear all,
I currently using postgresql v7.0.3
when i import text file to table with command "copy tablename from
'/tmp/a.txt';
and it shows
"copy: line 20, Cannot insert a duplicate key into unique index testpri_pk"
,then it exits with doing nothing.

I want to ignore this errors and continue copy the next record. How to do
that?
if I don't filter in '/tmp/a.txt' before using copy command.

Thank you so much for your help in advance .
Regards
Jaruwan