#!/usr/bin/perl
use strict;
use warnings;

# Might as well declare this early on and save some typing :)
my $s = "students.txt";

# *Always* check system operations for errors
open Fh, ">", $s or die "$s: $!\n";
print Fh "Perry*Steve*234\nSmith*Jane*456\nJones*Mary*567\n";
close Fh;

my (@bits, %pass);
# Don't guess at the error ahead of time - get the real story with '$!'
open Fh, "<", $s or die "$s: $!\n";
while(<Fh>) {
        @bits = split /\*/;
        $pass{join "_", @bits[0,1]} = $bits[2];
}

# Let's see what we got in the hash
printf "%s:\t%d\n", $_, $pass{$_} for sort keys %pass;