Please don't ignore requests to use <code> tags. You can edit your posts and add them. Having posted runnable code, the issues become more obvious: you open file "block.power" for writing, not reading--so use "<", not ">" (and you don't test whether the open succeeds). Your while loop loops infinitely over "$fh", which is always true; you should say while (<$fh>) {, which actually reads from the filehandle. The undefined variable in the pattern match is in fact $_.

I want to extract lines between Pattern1 and Pattern2 and write it into file2

untested

#!/usr/bin/perl 
use strict; 
use warnings; 
our $fh; 
our $log; 
open($fh,"<","block.power"); 
open ($log,">","temp.log")
or die "can not open file $log : $!\n" ; 
while($fh){
     if (/Pattern1>(.*?)<Pattern2/) {
              print $log $1;  
              }  
   } 
close $fh;
close $log;
[download]

Hi,

What you are doing will fail. When you slurp in a file using a while loop it is read in a line at a time.

You also need to add < an > around your file handle. In your example you are testing if $fh is defined. Your code will never break out of the loop. In the following code I open the input file, loop over it looking for the start pattern and then end pattern. I then use a var to toggle true/false Not the best way to do this however it works.

-Kiel R Stirling

#!/usr/bin/perl -w
use strict;

open IN, "/tmp/p.txt" or die $!;
open OUT, ">/tmp/temp.log" or die "can not open file log : $!\n" ;

my $start = 0;
while(<IN>){
        if (/<Pattern1/) {
                $start = 1;
                next;
        } elsif (/<Pattern2/) {
                $start = 0;
                next;
        }
        print OUT if $start;

}
close IN;
close OUT;
[download]

Thanks to all of you for your help. Based on your guidance i managed to get my code work. I'm posting my code below. #!/usr/bin/perl #use strict; #use warnings; my $fh; my $log; my $line; open($fh,"<","file1") or die "can not open file $fh : $!\n" ; open ($log,">","file2")or die "can not open file $log : $!\n" ; while($line = <$fh>) { if ($line =~ /pattern1/ ) { printf $log $line; while($line = <$fh>) { if($line =~ /pattern2/) { printf $log $line; last; } else { printf $log $line; } } } } close $fh; close $log; Happy to take your advice to make this code more efficient.