Reading from a file

Hi guys I'm hoping somebody can help me with what is probably quite an easy task for the experts out there!

Could somebody please tell what I need to add or change in the following code (I know the first line is gone straight away) so that instead of reading input from the keyboard the program will read from a file in my directory and then print the results to the screen.

Nothing is working for me so far, I reckon I'm probably just making silly mistakes so I'd appreciate a bit of help - ta v. much!

#!/usr/bin/perl

print "Please enter the heading of your text to be categorized \n";
chomp ($string = <STDIN>);
#chop $string;

  @aswordlist = qw(asthma inhale inhaler inhaled chest airway airways breath breathing breathe agonists exercise lung lungs nedocromil leukotriene);
  @word{ @aswordlist } = ();  # this is the %word hash

  while ($string =~ /(\S+)/g) {  # groups of non-whitespace characters
    if (exists $word{$1}) {      # $1 is that group of characters
      $word{$1}++;               # increment the times it was found
    }
  }

# variable that keeps a total of all the keywords found!!
$total_count=0;
   for (@aswordlist) {
      if ($word{$_}) {  # if there was at least 1 match for the word
             $total_count++;
       }
     }

# NOW, print the results..
print "$total_count asthma keyword(s) were found in the heading.\n";

if ($total_count > 0)
  {
     print "This text is probably related to asthma.\n";
   }
elsif ($total_count < 1)
   {
     print "This text is probably not related to asthma.\n";
   }