Change your conditionals. There's a myriad conditions your can use to your advantage: in the first case, since you're pulling the parameters off one by one you can check for whether @ARGV still has elements: 
my $MISC_FILE_DIR = @ARGV ? shift : die usage();
# ...
# ...

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But I'd rather write that piece as 
die usage() if @ARGV < 5;
my ($MISC_FILE_DIR, $req, $inqfile, $sent, $status) = @ARGV;

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Your second situation requires the canonical fix, a test of definedness: 
while( my @row = $sth->fetchrow_array ) {
        print join( '|', map ( defined() ? $_ : 'NULL', @row )) ."\n";
}

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Makeshifts last the longest.

In reply to Re: zero vs undef by Aristotle
in thread zero vs undef by Plankton

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