I think the OP is looking for something like this:

use strict;
use warnings;

my $input_file='file.txt';

while (1){ # Infinite loop
   print "Enter the word you are looking for (or 'quit' to exit): ";
   my $answer = <STDIN>;
   chomp $answer; # remove newline char from answer
   last if $answer =~/quit/i; # Exit loop
   print "Looking for '$answer'\n";
   my $found = 0;

   open my $f, "<", $input_file or die "ERROR: Cannot open $input_file
+ : $!";
   while (<$f>) {
      m/$answer/ or next;
      $found=1;
      last;
   }
   close $f;
   if ($found){
     print "Found $answer!\n";
   }else{
     print "Sorry - $answer was not found\n";
   }
}
[download]