#!/usr/local/bin/perl -w
use strict;
use Fcntl ':flock';
my $file = "inputdata.txt";
open(INFILE, $file) or die "File Not Found: $!";
flock(INFILE, LOCK_EX);
my @students;
while (<INFILE>) {
   push @students, [split / /, $_];
}
my %hash;

# where's $grades coming from?
# $hash{$grades}= $students[0]*0.2 + $student[1]*0.25+$students[2]*0.25 + $student
+s[3]*0.3;

# flock(INFILE, LOCK_UN); # don't use unlock, it's done automagically by close()
close(INFILE);