if ($#ARGV != 0) {
     print "One, and only one (not $#ARGV), command line parameter is expected\n";
     exit;
}

##</code><code>##

@ARGV == 1 or die "usage: $0 inputfile\n";

##</code><code>##

my $inputFile=$ARGV[0];

##</code><code>##

my $inputFile = shift;

##</code><code>##

if ( not -e $inputFile) {
     die "$inputFile doesn't exist!!!\nExiting.\n";
}

##</code><code>##

-f $inputFile or die "input file '$inputFile' does not exist.\n";

##</code><code>##

open my $file, $inputFile or die "Could not open $inputFile: $!";

##</code><code>##

open my $file, '<', $inputFile or die "Could not open $inputFile: $!";