Perl and pg_dump

This may not be the right place to post this question, but I had to start
somewhere.

I have a small perl script that is supposed to run pg_dump daily to backup
databases.
The script is called via the cron on a Redhat 6.1 system with PostgreSQL
6.5.

The error that I receive when cron attempts to run the script is:

Connection to database 'template1' failed.
FATAL 1: SetUserId: user 'root' is not in 'pg_shadow'

I know root isn't in pg_shadow, and I don't want it there (I _do_ know
better than to do things as root ;)).

How can I tell either Linux, PostgreSQL or the script to use another user
(Postgres?) to run the script?

A copy of the script is below.

TIA-
Jim
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#!/bin/sh

PSQL=/usr/bin/psql
DUMP=/usr/bin/pg_dump
PREFIX=`date +%j`
BACKUP_DIR=/data/pgsql/data

Databases=`$PSQL -tq -d template1 -c "select datname from pg_database"`
renice 20 $$

echo Backup started ...
for db in `echo $Databases`
do

echo "time: `date +%H%M%S` - Backup of $db in progress ..."
$DUMP -D $db > $BACKUP_DIR/$PREFIX.$db
echo "time: `date +%H%M%S` - Backup of $db finished ..."
done
echo Backup finished
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