sub compare_files($$$)
{
    my $FH1 = shift;
    my $FH2 = shift;
    my $OUTPUT_FH = shift;
    
    my @FILE1_ARRY = <$FH1>;
    my @FILE2_ARRY = <$FH2>;
    
    my $CMPR_ARRY_REF = \@FILE1_ARRY;
    my @CMPR_ARRY = @{$CMPR_ARRY_REF};
    my $CMPR_ARRY_NUMBER = 1;
    
    if ($#FILE1_ARRY > $#FILE2_ARRY)
    {
        print "FILE 1 is larger than FILE 2\n";
        print $OUTPUT_FH "FILE 1 is larger than FILE 2\n";
    }
    elsif ($#FILE1_ARRY < $#FILE2_ARRY)
    {
        print "FILE 1 is smaller than FILE 2\n";
        print $OUTPUT_FH "FILE 1 is smaller than FILE 2\n";
        $CMPR_ARRY_REF = \@FILE2_ARRY;
        @CMPR_ARRY = @{$CMPR_ARRY_REF};
        $CMPR_ARRY_NUMBER = 2;
    }    
    else
    {
        print "FILE 1 is the same size as FILE 2\n";
        print $OUTPUT_FH "FILE 1 is the same size as FILE 2\n";    
    }
    print "*"x70,"\n";
    print $OUTPUT_FH "*"x70,"\n";
    
    for(my $iter = 0; $iter <= $#CMPR_ARRY; $iter++)
    {
        if ( $CMPR_ARRY_NUMBER == 1 )
        {
            print "END OF FILE 2, BUT NOT FILE 1. STOPPING COMPARE AT 
+LINE ".($iter+1)." OF FILE 1\n" if ($iter > $#FILE2_ARRY);
            print $OUTPUT_FH "END OF FILE 2, BUT NOT FILE 1. STOPPING 
+COMPARE AT LINE ".($iter+1)." OF FILE 1\n" if ($iter > $#FILE2_ARRY);
            last if ($iter > $#FILE2_ARRY);        
            if ( quotemeta($CMPR_ARRY[$iter]) eq quotemeta($FILE2_ARRY
+[$iter]) )
            {
                print $OUTPUT_FH "Line ".($iter+1)." matches between b
+oth files\n";
            }
            else
            {
                print $OUTPUT_FH "Line ".($iter+1)." does NOT match be
+tween both files\n";
            }
        }
        else
        {
            print "END OF FILE 1, BUT NOT FILE 2. STOPPING COMPARE AT 
+LINE ".($iter+1)." OF FILE 2\n" if ($iter > $#FILE1_ARRY);           
+ 
            print $OUTPUT_FH "END OF FILE 1, BUT NOT FILE 2. STOPPING 
+COMPARE AT LINE ".($iter+1)." OF FILE 2\n" if ($iter > $#FILE1_ARRY);
            last if ($iter > $#FILE1_ARRY);        
            if ( quotemeta($CMPR_ARRY[$iter]) eq quotemeta($FILE1_ARRY
+[$iter]) )
            {
                print $OUTPUT_FH "Line ".($iter+1)." matches between b
+oth files\n";
            }
            else
            {
                print $OUTPUT_FH "Line ".($iter+1)." does NOT match be
+tween both files\n";
            }        
        }
    }
    print "*"x70,"\nCompare Complete.";
    print $OUTPUT_FH "*"x70,"\nCompare Complete.";
}
[download]

compare_files($FH1,$FH2,$OUTPUT_FH);
[download]

Hi VincentK, "you are comparing each line in your first file to every line in your second file"

Yes , i have a "config" file where i can configure the content of the file according to some element/name or etc. then this config file will search through another file(second file) line by line to check if the element/name from my config file exist or not. If yes, then the line will processed further, else if not then it will flag an error message.

"In this case, a match in the first file say on line two could match line 50 in file two ( or multiple lines if files contain duplicates ). Is this what you want?"

YES exactly, let say in the case of duplicate then it doesnt matter because it will be overwritten because i assigned it to a hash

Thank you for your help and the sub that you give as well. I can use the sub as well with a bit of tweak. Thank you

Do you have some example data of the files you are working with? Are you looking for exact matches, or will you want to be able to specify regex type patterns to match? Will the entire line match, or do you just need to find the target anywhere in the line?

Cheers,
R.

HI Random_Walk, yes you are right about the exact matches, i am just looking for a word that matched in a line of files.

Example of the element that i am looking for in a file

hlkout
[download]

Example of the line that matched the element

     .hlkout(hi_lkout[15:0])
[download]

from the line that matched my regex, i would further do some processing on it, to get something else like for this example i will be using the hi_lkout for another purpose which i dont describe here...

Does this, untested, code help?

use strict;
use warnings;
use Getopt::Long;
my ( $cfg,$files ); 
my $output = 'Output.summary';
GetOptions ('cfg=s' => \$cfg, 'rtl=s' => \$files); 
open my $fh1, '<', $cfg    or die "Can't open $cfg: $!"; 
open my $fh2, '<', $files  or die "Can't open $files: $!"; 
open my $fh3, '>', $output or die "Can't open $output: $!";

# Read the config file first 
# less memory required assuming it is the smaller file
my @patterns;
while (<fh1>) {
    next unless /\S/; 
    chomp;
    push @patterns, $_;
}

my %results;
# Now look through the other file
while (my $data = <$fh2>) {
  next unless /\S/;
  chomp $data;
  for my $pattern (@patterns) {
    if (index $data, $element) { # don't need regex for exact match
      $results{$data} = "matches $element";
      last;
    }
    else {
      $results{$data} = "doesn't match";
    }
  }
}

while (my($key,$value) = each(%results)) {
  print $fh3 "$key => $value\n";
}
[download]

Cheers,
R.