Hoping everyone had a great New Year and thanks for the replies. I started trying some more tactics to find out how to compare columns and lines. I am trying it as an exercise. There are actually not 50 files, but I meant it could be more than 2. Here are actual files I created: first.txt 
/vol/cat,feline
/vol/dog,canine
/vol/cat,feline
/vol/cat,feline
/vol/amphibian,FROG
/vol/amphibian,FROG

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second.txt 
9,/vol/elephant,fourfeet
1999,/vol/dolphin,fish
10,/vol/cat,feline
1111,/vol/goldfish,fish
2222,/vol/spider,arachnid
5555,/vol/camel,dromedary
3333,/vol/wolf,canine

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I am trying to do the following: 1. select the /vol/cat,feline as the element common in the array - this will require that the first column be excluded. 2. If the /vol/cat,feline is found (if an element is found in common to the array, print the ID # - for example #10. Here is what I did so far: 
use strict;

sub get_animal {
  open my $FILE, '<', shift or die $!;
  return map {chop; $_ => $_} <$FILE>;
}

my %a = get_animal '/tmp/first.txt';
my %b = get_animal '/tmp/second.txt';

{
  
  print "$_\n" for grep {$_} @a{keys %b};
}

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It works if the column with the numbers in it is deleted from second.txt. I don't know how to make it compare the first and second columns from first file with the second and third columns from the second file. After that, it needs to return the ID # when it finds a match. Any ideas?

In reply to Re^2: comparing multiple files for patterns -- oneliner explained by 2015_newbie
in thread comparing multiple files for patterns by 2015_newbie

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