#!/usr/bin/perl
use strict;
use warnings;
my $outfile="out.html";
my $final="final.txt";
open OUTFILE, "<$outfile";
open FINAL, ">$final";
while (<OUTFILE>) {
        s/<br>//gi;
        print FINAL if /(line\d*=(\d|[A-Za-z]{3}\s).)/;
}
[download]

line1=10
line3=20
line3=30
line4=Mon May 18 02:28:58 EDT 2009
line5=60
line6=Mon May 18 02:28:58 EDT 2009
line7=Mon May 18 02:28:58 EDT 2009
line8=Mon May 18 02:28:58 EDT 2009
line20=Mon May 18 02:28:58 EDT 2009
line30=60
line40=Jambalaya                #erroneous input, should not print to 
+final.txt
line100=45
line 200=Mon May 18 02:27:58 EDT 2009
line1000=Mon May 18 02:28:58 EDT 2009
line1001=90
line 2000=Mon May 18 02:28:58 EDT 2009         #erroneous input, shoul
+d not print to final.txt
line2001=100
line10000=50
line10001=Mon May 18 02:28:58 EDT 2009
[download]

line1=10
line3=20
line3=30
line4=Mon May 18 02:28:58 EDT 2009
line5=60
line6=Mon May 18 02:28:58 EDT 2009
line7=Mon May 18 02:28:58 EDT 2009
line8=Mon May 18 02:28:58 EDT 2009
line20=Mon May 18 02:28:58 EDT 2009
line30=60
line100=45
line1000=Mon May 18 02:28:58 EDT 2009
line1001=90
line2001=100
line10000=50
line10001=Mon May 18 02:28:58 EDT 2009
[download]

Thank you! it worked.I could even get rid of the duplicate lines.

one more question:can I use the same thing if the input file has lines like below:

line50=false
[download]

Is it the same file, or a different file that has line30=false? Either way, the regexp would need to be modified to account for that... maybe something like print FINAL if /(line\d*=(\d|[false]|[A-Za-z]{3}\s).)/;