exists statement not working perl - perl

Question

This is a homework assignment. I am not looking for the "code to make it work" more looking for a point in the right direction on where my logic is wrong.
use strict;
use warnings;
#rot13 sub for passwords
sub rot13{
my $result;
chomp(my $input = <STDIN>);``
# all has to be lower case
my $lower = lc $input;
my $leng = length $lower;
for(my $i = 0; $i < $leng; $i++){
my $temp = substr ($lower,$i,1);
my $con = ord $temp;
if($con >= '55'){
if($con >= '110'){
$con -= 13;
}
else{
$con += 13;
}
}
$result = $result . chr $con;
}
return $result;
};
#opening a file specified by the user for input and reading it
#into an array then closing file.
open FILE, $ARGV[0] or die "cannot open input.txt";
my #input = <FILE>;
close FILE;
my (#username,#password,#name,#uid,#shell,#ssn,#dir,#group,#gid);
my $ui = 100;
foreach(#input){
my ($nam, $ss, $gro) = split ('/', $_);
chomp ($gro);
$nam= lc $nam;
I created a hash so I can use the exists function then using the function and if it does exist go to the next round of the loop. I feel like I am missing something with this.
my %nacheck;
if( exists ($nacheck { '$nam' } )){
next;
}
$nacheck{ "$nam" } = 1;
while (my ($key, $value) = each %nacheck){
print "$key => $value\n";
}
All this works for now but any tips on how to do it better would be appreaciated
my($unf, $unm, $unl) = split (/ /, $nam);
$unf = (substr $unf,0,1);
$unm = (substr $unm,0,1);
$unl = (substr $unl,0,1);
my $un = $unf . $unm . $unl;
if(($gro) eq "faculty"){
push #username, $un;
push #gid, "1010";
push #dir, "/home/faculty/$un";
push #shell, "/bin/tcsh";
}
else{
my $lssn = substr ($ss,7,4);
push #username, $un . $lssn;
push #gid, "505";
push #dir, "/home/student/$un";
push #shell, "/bin/bash";
}
#pushing results onto global arrays to print out later
push #ssn, $ss;
my $pass = rot13;
push #password, $pass;
push #name, $nam;
push #uid, $ui += 1;
}
#printing results
for(my $i = 0; $i < #username; $i++){
print
"$username[$i]:$password[$i]:$uid[$i]:$gid[$i]:$name[$i]:$dir[$i]:$shell[$i]\n";
}

Answer 1

The value of the expression '$nam' is those four characters themselves. The value of the expression "$nam" is whatever the value of the variable $nam is, expressed as a string.
Double quotes allow string interpolation. Single quotes do not; you get exactly what you type.

Answer 2

As you've written it:
my %nacheck;
if( exists ($nacheck { '$nam' } )){
next;
}
$nacheck{ "$nam" } = 1;
the %nacheck is newly created and must be empty. Therefore the exists test fails.
Or have you just shown the definition adjacent to the test for the purpose of the example?
If so, can you show us what your code actually looks like?
Edit: Also, as Charles Engelke noted, you've used single-quotes around a variable '$nam' which is wrong.