Trying to process the two files in parallel is a bad idea. Assuming that text2 is not huge, read it first and create a hash entry for each file entry.

Then read text1 and use the hash to check to see if there is a matching entry in text2:

use strict;
use warnings;

my $text1 = <<'END_TEXT';
2343/45/45/cal/ca-1.xml     2343/45/45/ca-1
6534/534/34/car/ca-5.xml     6534/534/34/ca-5
END_TEXT

my $text2 = <<'END_TEXT';
6534/534/34/ca-5
5676/435/734/da-1
END_TEXT

my %text2Entries;

# Build a hash table of text2 entries
open my $inFile, '<', \$text2 or die "Unable to read text2: $!\n";
while (<$inFile>) {
    chomp;
    ++$text2Entries{lc $_};
}
close $inFile;

# Read the text1 entries and print any that don't have a text2 entry
open $inFile, '<', \$text1 or die "Unable to read text1: $!\n";
while (my $line = <$inFile>) {

    my ($part1, $part2) = split /\s+/, $line;

    chomp $part2;
    next if ! exists $text2Entries{lc $part2};
    print $line;
}
close $inFile;
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Prints:

6534/534/34/car/ca-5.xml     6534/534/34/ca-5
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Don't get hung up on the two $text strings - that's just so I can provide a runnable test script without requiring external files.

This is a great idea. I would just add a few comments that might clarify a few things for previous posts.

1. split /\s+/, $line; splits on any whitespace character, this includes space,\f,\r,\n,\t. Since \n is in this set, you don't need to chomp($part2); doesn't hurt but it is not necessary here. The reason in previous post that "\t" didn't work is that you need a regex for the first arg to split./\t/ would have worked but /\s+/ is usually better. The \t idea would result in a \n in $part2 and of course since you can't see these non-printing characters it is possible that there is are some plain spaces in there!

2.The best way to get the 2nd thing from the split is with list slice. my $part2 = (split /\s+/, $line)[1]; Since you don't use $part1, there is no need to assign it. It often occurs that you are working with a line with a bunch of things on it and you just want a couple of them. Using list slice allows you to assign meaningful names to these things like maybe: my($temperature,$city)=(split /\s+/,$line)[3,8];. This is a lot better than say, $line[3] because you don't need any comments to explain that thing 3 means temperature.

Of course here the op probably has some other name in mind for $part2 that would make the code even more clear.

The files are very huge. I tried something like

open FH, '<file1.txt';
@data = <FH>;

open FH1, '<file2.txt';
@data1=<FH1>;

my $text1 = <<END_TEXT;
@data
END_TEXT

my $text2 = <<END_TEXT1;
@data1;
END_TEXT1
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@data inside <<END_TEXT prints only one row. How can I print entire array inside <<END_TEXT

How about this:

use strict;
use warnings;
my %required;
open(IN,"<","text2.txt") or die;
while(<IN>){
   chomp;
   $required{$_}++
}
close IN;
open(IN,"<","text1.txt") or die;
while(<IN>){
   if (/\S+\s+(\S+)/ && !exists $required{$1}) {
      print "$1 doesnot match in text1.txt. Please help me.\n"
   }
}
close IN;
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Hi, How to extract only second field from the text1.txt

open(FILE1, 'text1.txt');
open(FILE2, 'text2.txt');
while ($line = <FILE1>) {
@lines=split("\t",$line);
print $lines[1];
        if($lines[1] != <FILE2>){
#       print "$line";
        }
}
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I tried something like this. But split doesnot works here. How can I check <FILE2> with second column of text1.txt

Hi,
Try this..


open(FILE1, 'File1.txt');
open(FILE2, 'File2.txt');
while ($line = <FILE1>) {

    @lines=split(' ',$line);

    print $lines[1];

    if($lines[1] != <FILE2>){
        print "$line";
    }
}
[download]

In split use space as a delimiter, that will exactly splits the line.