use warnings;
use strict;
use File::Find;

open (OUT, ">C://strings.txt");

my $search_string = 'http';
find( \&grep, "C:\\Program Files\\whatever" );

sub grep
{
    my $file = $File::Find::name;
    if ( -f $file && -r _ ) {
        open( my $fh, "<", $file ) or return;
        while ( my $rec = <$fh> ) {
        print OUT "$rec" #in $_\n"
              if $rec =~ /$search_string/;
        }
    }
}
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