use IO::Handle;
use File::Temp;
use File::Spec;
use autodie;

my $file = $ARGV[0];

my $temp = File::Temp->new(DIR => File::Spec->curdir);
open my $fh, '<', $file;
while ( my $line = $fh->getline ) {
    if ( $fh->input_line_number % 2 ) {
        $temp->print($line);
    }
}
close $fh;

rename $temp->filename, $file;