system ("su -l - $user -c \'$action > DBlist.txt && cat DBlist.txt\'");

##</code><code>##

system ("su -l - MyRealuser -c \'$action > DBlist.txt && cat DBlist.txt\'");

##</code><code>##

print ">>>$user<<<\n";

##</code><code>##

>>>some_username<<<

##</code><code>##

>>>some_username
<<<

##</code><code>##

chomp(my $user = $line);

##</code><code>##

while(my $exec_line = <EXEC>) {
    ...
    while (my $cmd_line = <$cmd>) {
        ...
    }
}