open my $TEMPF, '>', 'tempfile.tmp' or die("Unable to write to tempfile");

print $TEMPF $file_contents;
close $TEMPF;

open my $TEMPF, '<', 'tempfile.tmp' or die("Can't read tempfile back in");
while (chomp (my $line = <$TEMPF>)) {
   next unless $line =~ /^06/; #skip unneeded lines
   chomp(my $line2 = <$TEMPF>);
   #process lines
}
close $TEMPF;

unlink('tempfile.tmp');