Finding symbols in files using Perl

I am new to Perl and trying to learn it. I have two files, 'file1' and 'file2', I need to find which symbols in 'file1' are not in 'file2' for companyA and departments B and C.

File1

GTY
TTY 
UJK
TRE

File2

departmentA_companyA.try=675 UJK 88 KKR
departmentA_companyB.try=878 UJK 37 TAR
departmentA_companyC.try=764 UJK 92 PAM
departmentB_companyA.try=675 UJK 88 KKR
d开发者_运维知识库epartmentB_companyB.try=878 UJK 37 TAR
departmentB_companyC.try=764 UJK 92 PAM
departmentC_companyA.try=675 UJK 88 KKR
departmentC_companyB.try=878 UJK 37 TAR
departmentC_companyC.try=764 UJK 92 PAM

1. Create a list of all the symbols in file1
2. Go through file2. If the criteria matches, delete the symbol from the list.

In this case, I'd suggest you use the keys of a hash to store this list ($symbols{$symbol} = 1;). This is because it's easy and cheap to delete from a hash (delete $symbols{$symbol};).

Spoiler:

use strict;
use warnings;
use feature qw( say );

my %symbols;
{
   open(my $fh, '<', 'file1')
      or die("Can't open file1: $!\n");

   while (<$fh>) {
      chomp;
      ++$symbols{$_};
   }
}

{
   open(my $fh, '<', 'file2')
      or die("Can't open file2: $!\n");

   while (<$fh>) {
      chomp;
      my ($key, $val) = split /=/;
      my ($dept, $co) = split /[_\.]/, $key;
      if ($co eq 'companyA' || $dept eq 'departmentB' || 'departmentC') {
         my @symbols = split ' ', $val;
         delete @symbols{@symbols};
      }
   }
}

say for keys %symbols;

You can use a hash to count the number of times each symbol appears in the file, then print the ones that have a count of 0.

use strict;

open SYMS, $ARGV[0] || die;
open INFILE, $ARGV[1] || die;

my %symbols;

while (<SYMS>) {
    chomp;
    $symbols{$_} = 0;
}

while (<INFILE>) {
    my @F=split;
    next unless $F[0] =~ /companyA/;
    next unless $F[0] =~ /department[BC]/;
    ++$symbols{$F[1]} if (defined $symbols{$F[1]});
    ++$symbols{$F[3]} if (defined $symbols{$F[3]});
}

for my $symbol (keys %symbols) {
    print "$symbol\n" if $symbols{$symbol} == 0;
}