Test for file exists?

I want to use pgsql to send the command:

Copy sometable from 'sometable.csv';

But only if 'sometable.csv' exists;

If 'sometable.csv' does not exist as an input table I want to continue
the next command.

My full procedure is as follows and any help is greatly appreciated.

Thanks

Richard

CREATE OR REPLACE FUNCTION restore_database(text)
RETURNS text AS
$BODY$
declare
tblname record;
cnt record;
tname varchar :='';
tquery varchar :='';
filename varchar :='';

begin
tname := '';
for tblname in select tablename from pg_tables WHERE not(tablename like
'pg_%') and not(tablename like 't_%')
and not(tablename like '%_list') order by tablename loop
raise notice '%',tblname.tablename;
tquery := 'delete from ' || tblname.tablename ;
execute tquery;
filename := '/'||$1||'/'|| lower(tblname.tablename)||'.csv';
tquery := 'copy ' || tblname.tablename || ' from ' ||
quote_literal(filename);
execute tquery;
end loop;

return tquery;
end;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;

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