This wouldn't delete lines from your original file, but at least splits it in two separate ones.
Note that it relies on your input being formatted as your example data. 
use strict;

open OF1, ">var2_equal_to_3.txt";
open OF2, ">var2_not_equal_to_3.txt";
my ($flipflop, $flag, $prev);
while (<DATA>) {
    chomp;
    $flag = 1 if m/var2\s+=\s+3/i;
    $flipflop = /<rec\s+[0-9]+>/i .. /<\/rec\s+[0-9]+>/i;
    $prev = $_ if $flipflop == 1;
    if ($flag) {
        print OF1 "$prev\n"  if $flipflop == 2;
        print OF1 "$_\n";
    }else{
        print OF2 "$_\n";
    }
    $flag  = $prev = undef if $flipflop =~ /E0$/;
}

close OF1;
close OF2;

[download]
__DATA__
<Rec 1>
var2 = 5
some text
some text
some text
some text
</Rec 1>
<rec 2>
var2 = 3
some text
some text
some text
some text
some text
some text
some text
some text
</Rec 2>
<Rec 3>
var2 = 7
some text
some text
some text
some text
some text
some text
</Rec 3>
<rec 4>
var2 = 3
some text
some text
some text
some text
some text
some text
some text
some text
</Rec 4>

[download]
HTH
--
Olivier

In reply to Re: help: extracting multiple lines from file based on match in one line by olivierp
in thread help: extracting multiple lines from file based on match in one line by my_perl

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