You could so something like (following code is untested, just shown here to guide you, not for cut-and-paste purposes):

use AnyDBM_File;
use Fcntl;

my $pattern_file = "whatever 1";
my $target_file  = "whatever 2";
 
my $dbm          = "/tmp/matchdbm";
 
tie my %db => AnyDBM_File => $dbm, O_CREAT | O_RDWR, 0666
        or die "Failed to tie to $dbm: $!";
 
open my $pf => $pattern_file or die "Failed to open $pattern_file: $!"
+;
open my $tf => $target_file  or die "Failed to open $target_file: $!";
+  
 
$db {$_} ++ while <$pf>;               
 
my @buff = ("", "", "");
 
while (<$tf>) {
    @buff = (@buff [1, 2], $_);
    print @buff if $db {$buff [1]};
}
@buff = (@buff [1, 2], "");
print @buff if $db {$buff [1]};
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Abigail

I have come to discover that using regex is quite slow

_________
broquaint

It's not clear from your question, but do you even need to use pattern matching at all? If what you're trying to match (the lines from the first file) are fixed strings, a simple eq will do the job.

It may be obvious and not apply to what you're doing, but I wanted to point it out, because it's very common that people over-use pattern matching when a simple string compare will suffice.

Dr. J

I started writing this up earlier today, but I had to leave it to do some work. When I came back to post I saw that Abigail had already posted a solution. This solution may not be as fast as her's but it is cut and paste-able. If you want to use it feel free

I also tried to make it simple as possible.

Thanks,
Kristofer

#!/bin/perl -w

use diagnostics;
use strict;
use warnings;

############################################################
sub getAllLinesFromAFileandReturnItAsAnArray($)
{
my ($FILE) = $_[0];

  #Redundant check. This code should be unreachable just by
  #the way I defined this sub '($)'. I do manual checking
  #of each varible as an anal principle. Just my style - Kristofer
  if (!defined($FILE)) { die ("I did not receive a filename"); }

 open my $FileDescripter => $FILE or die "Could not open '$FILE'\n";
  my @ListOfStringsToReturn = <$FileDescripter>;
  close $FileDescripter;
  
  chomp @ListOfStringsToReturn;

#  my @ListOfStringsToReturn = ();
#  open (FileDescripter, "$FILE");
#  while (<FileDescripter>)
#  {
#    if (defined($_))
#    {
#      chop;
#      push @ListOfStringsToReturn, $_;
#    }
#  }
#  close(FileDescripter);


return @ListOfStringsToReturn;
}
#===========================================================

my $FirstFile = "FileOne.txt";
my $SecondFile = "FileThree.txt";
my @FileOne = getAllLinesFromAFileandReturnItAsAnArray($FirstFile);
my @FileTwo = getAllLinesFromAFileandReturnItAsAnArray($SecondFile);

for (my $i = 0; $i < @FileOne; $i++)
{
  print "Comparing Line $i in $FirstFile ... ";
  my $test = undef;
  for (my $j = 0; $j < @FileTwo; $j++)
  {
    if ($FileOne[$i] eq $FileTwo[$j])
    {
      print " matched to line $j in $SecondFile\n";
      print "  FileOne: '$FileOne[$i]'\n";
      print "  FileTwo: '$FileTwo[$j]'\n";
      #Setting j to @FileTwo will kill this loop
      $j = @FileTwo;
      $test = 0;
    }
  }
  if (!defined($test))
  {
    print " not matched. Compared to $#FileTwo entries\n";
  }
}
[download]

Please, please, please. Reading in all lines of a file into an array is standard idiom. Do not use such a silly, inefficient, routine. And NEVER EVER forget to check the return value of open.

Here's how you read the file into an array:

    open my $fh => $file or die "Open failed: $!";
    my @array = <$fh>;
    close $fh;
[download]

If you want to chomp of newlines, add the following line:

    chomp @array;
[download]

Don't reinvent the wheel. And don't code perl primitives in Perl.

Abigail