my @params = ();   
while ( my $param = shift ) {   
push @params, $param;   
}   
unless ( scalar @params == 4 ) {   
print "$0 <input fasta file> <block size> <block label> <output file>\n";   
exit;   
}   
my ( $inputFile, $blockSize, $blockLabel, $outputFile ) = @params;   
print "Input seems to be valid. Now I will try reading the contents of $inputFile...";

 print "$0 <input fasta file> <block size> <block label> <output file>\n" and die unless $ARGV == 4;  
my ( $inputFile, $blockSize, $blockLabel, $outputFile ) = @ARGV;