my $Usage = "Usage: $0 --min MIN --max MAX --in INFILE --out OUTFILE\n";

my %args;
while ( @ARGV >= 2 ) {
   if ( $ARGV[0] =~ /^--(min|max|in|out)$/ ) {
      my $opt = substr( shift, 2 );
      $args{$opt} = shift;
   } else {
      last;
   }
}
die $Usage if ( @ARGV or ( keys %args != 4 ));
# all 4 args are mandatory, and only these 4 args are allowed

# now use $args{in} instead of $input, etc...