if (open(FH, $file))
{
    ...complicated logic extending many many lines....
    close(FH);
}
else
{
    warn "Couldn't open $file: $!"\n";
}

##</code><code>##

unless (open(FH, $file))
{
    ...send email, sound the klaxons, raise a ruckus, etc.
    ...if I really can't continue, I'll die or exit here.
}
else
{
    ....do fun stuff with FH
}