password option in pg_dumpall

is there anyway of specifying password in the command line interface
of pg_dumpall??

this my script, and it asks for password for every host...
thanks

'''
#!/bin/sh
for line in `cat /home/mark/work/infrastructure/farm_all`
do
pg_dumpall -h $line -U postgres | bzip2 > "$line.bz2"
done
'''